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THE   NATUKE   AND  WORK 
OF   PLANTS 


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THE  NATURE  AND  WORK 
OF  PLANTS 

An  Introductio7i  to  the  Study  of  Botany 


BY 


DANIEL  TREMBLY  MACDOUGAL,  Ph.D. 

DIRECTOR  OF  THE   LABORATORIES,   NEW  YORK 
BOTANICAL    GARDEN 


THE   MACMILLAN   COMPANY 

LONDON :  MACMILLAN  &  CO.,  Ltd. 

1900 

All  rights  reserved 


COPYKIGHT,   1900, 

By  the  MACMILLAN  COMPANY. 


Nortoooi  ^tesB 
J.  S.  Gushing  &  Co.  -  Berwick  &  ! 
Norwood  Mass.  U.S.A. 


PREFACE 

The  course  outlined  in  this  little  book  is  essen- 
tially a  study  of  the  functions  or  action  of  the 
plant,  and  organs  are  considered  chiefly  as  instru- 
ments for  the  performance  of  work,  with  but  little 
attention  to  their  morphology.  It  is  believed  that 
this  method  of  introduction  to  the  subject  of  botany 
will  be  best  suited  for  beginners  who  have  not  at 
hand  the  facilities  of  a  laboratory.  In  conformity 
with  this  idea,  the  use  of  technical  terms  has  been 
restricted  to  the  actual  necessities  of  logical  treat- 
ment, and  the  demonstrations  have  been  developed 
by  the  simplest  experimental  methods. 

Material.  —  The  apparatus  needed  to  carry  out 
the  work  may  be  found  in  any  household,  with  the 
exception  of  the  hand  lens,  which  may  be  purchased 
for  less  than  a  dollar;  a  glass  wdiich  will  magnify 
six  to  ten  times  will  be  sufficient.  A  supply  of 
plant  material  is,  of  course,  indispensable.  Stu- 
dents having  access  to  greenhouses  will  be  able  to 

QKnu 


vi  PREFACE 

secure  specimens  to  illustrate  the  entire  course  with- 
out difficulty.  If  the  plants  of  the  woods  and  fields 
are  to  be  used,  as  many  observations  as  possible 
should  be  carried  out  in  the  summer,  spring,  and 
autumn,  and  a  supply  of  roots,  corms,  tubers,  bulbs, 
seeds,  and  fruits,  should  be  collected  for  use  during 
the  winter  season.  Many  of  these  may  be  preserved 
in  the  same  manner  as  potatoes,  and  forced  to  grow 
when  brought  into  a  warm  living-room  in  January 
or  later.  This  may  be  done  with  the  material  used 
in  the  following  paragraphs:  8,  10,  13,  19,  26,  38, 
39,  43,  44,  45,  46,  47,  48,  50,  51,  53,  54,  77,  97, 106, 
108,  109,  120,  129, 148, 165, 167, 168, 169, 180, 181, 
182,  183,  184,  185,  195,  211,  212,  213,  214,  216, 
217,  225,  and  229. 

Desirable  material  may  be  obtained  from  dealers 
in  native  plants  if  the  student  is  unable  to  collect  it 
himself.  It  is  quite  imj)ortant  that  the  plants  used 
should  be  properly  identified,  and  this  may  be  done 
by  the  use  of  a  manual  of  the  flora  of  the  region  in 
which  the  work  is  done,  which  may  be  selected  from 
the  following  list :  — 

Britton    and    Brown,   Flora   of    the   Nortliern   States   and 
Canada,  Charles  Scribner's  Sons,  New  York. 


PREFACE  Vll 

Gray,  Manual   of    Botany,  American   Book  Company,  New 

York  City. 
Chapman,  Flora  of  the  Southern  States,  Cambridge  Botanical 

Supply  Company,  Cambridge,  Mass. 
Coulter,  Flora  of  Western  Texas,  United  States  Department 

of  Agiiculture,  Washington,  D.  C. 
Greene,  Manual  of  Botany  of  the  Region  of  San  Francisco 

Bay,  Cubery  &  Co.,  San  Francisco. 
Howell,  Flora  of  Northwest  America. 
Coulter,  Manual  of  Eocky  Mountain  Botany,  American  Book 

Company,  New  York  City. 
Gray,   Field,   Forest,   and   Garden   Botany,  American   Book 

Company,  New  York  City. 

It  will  also  be  found  profitable  to  read  the  dis- 
cussions of  the  various  subjects  in  the  following 
works,  which  may  also  suggest  furtlier  lines  of 
experimentation :  — 

Kerner  and  Oliver,  Natural  History  of  Plants,  Holt  &  Co., 

New  York  City. 
Coulter,  Plant  Relations,  D.  Appleton  &  Co.,  New  York  City. 
Barne.s,  Plant  Life,  Holt  &  Co.,  New  York  City. 
Bailey,  Lessons  with  Plants,  Macmillan  Company,  New  York 

City. 
Atkinson,  Elementary  Botany,  Holt  &  Co.,  New  York  City. 
MacDougal,  Experimental   Plant   Physiology,   Holt   &   Co., 

New  York  City. 
Arthur  and  MacDougal,  Living  Plants  and  their  Properties, 

Morris  &  Wilson,  Minneapolis. 


VlU  PREFACE 

The  author  acknowledges  substantial  aid  from  Pro- 
fessor Francis  E,  Lloyd  in  the  revision  of  the  man- 
uscript and  the  reading  of  proof,  and  many  valuable 
suggestions  from  Mrs.  E.  G.  Britton. 

D.  T.  McD. 

New  York  Botanical  Garden, 
January,  1900. 


CONTENTS 


I.    The  Composition  and  Purposes  of  Plants 

1.  The  plant  is  composed  of  living  matter       .... 

2.  The  purposes  of  plants 

3.  Great  differences  among  plants 

4.  The  oaks,  maples,  elms,  ferns,  mosses,  and  pond-scums  are 

not  all  of  the  same  kind  among  themselves    . 

5.  A  species 

6.  Scope  of  w^ork  described 


PAGE 

1 


II.    The  Material  of  which  Plants  are  made  up 


§    7. 


§10. 
§11. 
§12. 
§13. 
§14. 
§15. 
§  16. 
§17. 
§18. 


The  plant  is  an  engine 

Water,  charcoal,  and  ash 

Leaves  shrink  in  drying 

Mineral  coatings  .... 

Uses  of  mineral  coatings 

Aquatic  plants  with  mineral  coatings 

Water  cultures,  with  and  without  mineral  salts 

Ash  or  mineral  salts  in  the  water  of  streams 

Elements  found  in  plants     .... 

Substances  serving  as  food  .... 

Compounds  in  the  plant       .... 

Tests  for  the  contents  of  plants   . 


III.     The  Manner  in  which  Different  Kinds  of  Work 

ARE    divided   among    THE   MEMBERS   OF    THE   BODY 

§  19.   Kinds  of  work,  or  functions  of  the  plant     ....       21 
§20.   Organs 22 


X  CONTENTS 

PAGE 

§  21.   Tissues 22 

§  22.   Method  of  study  of  functions  and  organs    ....      23 


IV.    The  Roots 

§  23.  Functions  of  roots 24 

§  24.  Roots  hold  the  stem  firmly  in  position        ....  24 

§  25.  Roots  were  first  developed  for  fixation        ....  26 

§  26.  Shrinkage  of  roots  to  aid  in  fixation 27 

§  27.  The  structure  of  the  root 28 

§  28.  Climbing  roots 28 

§  29.  Stilt  roots 29 

§  30.  Columnar  roots 29 

§  31.  Keel  or  ballast  roots 30 

§  32.  Substances  of  which  the  soil  is  composed   .        .        .        .  .30 

§  33.  The  soil  and  root-hairs  adhere 31 

§  34.  Root-hairs  and  the  region  from  which  they  arise        .         .  31 

§  35.  Action  of  roots  which  have  been  deprived  of  hairs     .         .  32 

§  36.  Can  water  be  taken  through  the  leaves  ?     .         .         .         .33 

§  37.  The  manner  in  which  root-hairs  take  in  liquids          .         .  34 

§  38.  Action  of  sugar 35 

§  39.  Another  method  of  imitation  of  the  action  of  root-haii-s    .  35 

§  40.  Action  of  root-hairs  on  particles  of  mineral  substance        .  36 

§  41.  The  fate  of  the  particles  of  soil 37 

§  42.  Food-material  in  the  soil,  and  how  the  plant  finds  it          .  38 
§  43.  The  tips  of  primary  or  main  roots  point  downward    .         .  39 
§  44.  The  tips  of  branches  of  the  main  roots  are  directed  hori- 
zontally      39 

§  45.  Sensitiveness  of  the  roots  to  moisture          ....  40 

§  46.  Roots  bend  away  from  light 41 

§  47.  The  tip  of  the  root  is  protected  by  a  sheathing  cap    .         .  42 

§  48.  The  sensitiveness  of  roots  to  touch  with  solid  objects         .  43 

§  49.  The  roots  of  air-plants 44 

§  50.  Parasitic  roots 45 

§  51.  IMethod  of  germination  and  growth  of  the  dodder      .         .  46 

§  52.  Union  of  roots  with  fungi 47 

§  53.  Roots  as  storage  organs 48 


CONTENTS 


§  54.   Method  of  growth  of  roots .49 

§  55.    Absorbing  and  fixing  organs  of  the  lower  plants         .         .       50 
§  56.    Absorbing  and  fixing  organs  of  the  ferns,  mosses,  and 

liverworts 50 

§  57.   Method  of  fixation  of  the  moulds  and  mushrooms      .        .      51 


v.    The  Leaves 

§  58.  Absorption  and  fixation  by  the  algae  and  bacteria      .        .  52 

§  59.    Structure  of  leaves 54 

§  60.   Leaves  with  both  surfaces  alike 56 

§  6L   Compound  leaves 56 

§  62.    Composition  of  the  air 57 

§  63.    Gases  of  use  to  the  plant 57 

§  64.    Functions  of  the  leaf 58 

§  65.    The  colors  of  leaves 58 

§  60.   Hidden  chlorophyl 59 

§  67.   Characteristics  of  chlorophyl 60 

§  68.   Spectrum  of  chlorophyl 60 

§  69.  The  leaf  is  a  machine  or  mill 61 

§  70.  Quality  of  light  most  useful  to  the  plant     ....  61 

§  71.   Light  destroys  chlorophyl 62 

§  72.  Light  is  necessary  for  the  formation  of  chlorophyl  in  most 

instances 62 

§  73.  Capacity  of  leaves  for  the  absorption  of  light     ...  63 

§  74.  Formation  of  food  in  chlorophyl-bearing  organs         .         .  64 

§  75.    iSTon-green  colors 65 

§  76.    Origin  of  red  colors 65  • 

§77.   Changes  in  color 66" 

§  78.    Autumnal  colors 67' 

§  79.   Uses  of  autumnal  colors 68 

§  80.  Uses  of  red  and  other  colors  in  flowers  and  fruits       .         .  68 

§  81.  Characteristics  of  red  and  blue  colors          ....  69 

§  82.   Red  color  as  a  shield 69 

§  83.  Red  color  as  a  heat  producer        .         .     '    .         .        .         .69 

§  84.   Red  color  as  a  heat  saver 70 

§  85.    Hairs  as  a  protection  to  a  leaf 71 


Xll  CONTENTS 

PAGE 

§    86.   White  surfaces 71 

§    87.   The  positions  of  leaves 72 

§    88.   Length  of  petioles 72 

§    89.   Leaf  mosaic 72 

§    90.    Getting  in  the  proper  position 73 

§    91.    Heliotropic  movements 73 

§    92.   Movements  of  leaves  and  stems  in  response  to  gravity      .  74 

§    93.   Movements  to  avoid  injury 74 

§    94.   Compass  plants 75 

§    95.   Some  plants  have  lost  the  power  of  manufacturing  chlo- 

rophyl 76 

§    96.    An  association  without  chlorophyl 77 

§    97.   Pitchered  leaves 77 

§    98.    Food-building  in  the  lower  forms 80  " 

§    99.   The  leaf  and  water 81  - 

§  100.   Course  of  the  water  in  the  leaf 81 ' 

§  101.   Transpiration 82  - 

§102.   The  vapor  transpired 82- 

§  103.    Measurement  of  the  amount  of  water  thrown  off  by  a 

plant 83- 

§  104.   Sunlight  increases  transpiration 83 

§  105.    Regulation  and  control  of  transpiration     ....  84 
§  106.    Wax  or  bloom  as  a  means  of  prevention  of  excessive  loss 

of  water 84- 

§107.    Size  of  leaves  and  dryness  of  the  air  ....  84- 

§  108.    Sleep  movements 85 

§  109.   Velvety  surfaces 85 

§  110.    Autumnal  leaf  fall 86 

§  111.   Separatory  laj^er 86 

§  112.   The  length  of  life  of  leaves 87 

§  113.   Growth  of  leaves 87 

§  114.   Wilting 88 

§  115.   Transplanting  trees  and  herbs  is  attended  by  wilting       .  89 

§  116.   Freezing  and  frosting 89 

§  117.    The  air  is  colder  on  a  frosty  night  near  the  surface  than 

it  is  a  few  feet  above  it 91 

§  118.   Drainage  of  cold  air 92 


CONTENTS 


VI.    Stems 


§119. 
§120. 
§  121. 
§122. 
§  123. 
§124. 
§  125. 
§  126. 
§  127. 
§  128. 
§  129. 
§  130. 
§131. 
§132. 
§133. 
§134. 
§135. 
§136. 
§137. 
§138. 
§139. 
§140. 
§141. 
§142. 
§  143. 
§144. 
§145. 
§146. 
§147. 
§148. 
§149. 
§150. 
§151. 
§152. 
§153. 


The  nature  of  stems 

Stems  are  made  up  of  sections  or  internodes 
Branches  arise  at  the  nodes  or  joints  only 
Relation  of  the  leaves  and  branches  . 

Leaf  traces 

Relation  of  leaves  and  flowers   . 
Structure  of  stems      .... 

Uses  of  stems 

Methods  by  which  firmness  is  secured 
Arrangement  of  dead  cells  to  secure  firmness  of  stems 
Arrangement  of  mechanical  tissues  in  a  stem  of  a  grass 
Mechanical  tissues  in  a  sunflower  stem 
Mechanical  tissues  in  a  cai-nation  stem 
Arrangement  of  mechanical  tissues  in  a  petiole 
The  firmness  of  plants  that  become  limp  when  dried 
Stems  as  conducting  organs 

Upward  path  of  sap 

Path  of  sap  in  large  trees  .... 

Girdling 

Downward  path  of  material  from  the  leaf 

Forces  which  carry  the  sap  upward  through  the  stem 

Root,  or  bleeding  pressure 

The  flow  of  sap  of  the  sugar  maple   . 

Dew 


How  to  cause  a  plant  to  form  dew  at  any  time 
Lifting  power  of  leaves  and  branches 
Growth  of  stems  .... 

Action  of  embryonic  tissue  of  a  tree 
Growth  in  length  and  diameter 
Measurement  of  growth  in  length 
Measurement  of  growth  in  diameter 

The  bark 

Growth  of  a  corn  stem 

Nodding  or  circular  movements  due  to  unequal  growth 

Length  of  life 


XIV  CONTENTS 

PAOB 

§  154.  Annuals 113 

§  155.  Biennials 114 

§  156.  Perennials 114 

§  157.  Changes  in  the  length  of  life  of  a  species          .        .        .  115 

§  158.  Buds 115 

§  159.  Naked  buds 116 

§  160.  Scaly  buds 116 

§  161.  Buds  of  the  apple 117 

§  162.  Buds  of  elder,  maple,  or  elm 118 

§  163.  Sleeping  buds 118 

§  164.  The  awakening  of  sleeping  buds 118 

§  165.  Winter  buds  of  aquatic  plants 119 

§  166.  Behavior  of  the  hibernacula 120 

§  167.  Bulbs 121 

§  168.  Corms 121 

§  169.  Forcing  or  inducing  an  earlier  growth       ....  121 

§  170.  Some  protective  devices  of  the  shoot  .         .         .         .122 

§  171.  Branches  used  as  leaves 124 

§  172.  The  part  of  stems  in  the  struggle  for  existence         .         .  124 

§  173.  Weeds 125 

§  174.  Climbing  plants 125 

§  175.  The  irritability  or  sensitiveness  of  stems  ....  127 

§  176.  Sensitiveness  to  gravity 128 

§  177.  Stems  are  found  among  the  higher  plants  only         .        .  129 


VII.    The  Way  in  which  New  Plants  Arise 

§  178.   Distribution  of  the  individuals  of  a  species       .         .         .  130 

§  179.   Methods  of  reproduction 131 

§  180.   Reproduction  by  cuttings 132 

§  181.    The  stem  may  reproduce  the  entire  plant          .         .         .  132 
§  182.    The  root  may  reproduce  the  entire  plaut  ....  132 
§  183.    Structures  used  by  plants  as  means  of  vegetative  repro- 
duction       133 

§  184.   Tubers 133 

§  185.   Bulbils  and  bulblets 134 


CONTENTS 


XV 


§  186.    Division  of  the  body  by  the  death  of  part  of  it 
§  187.   Division  among  the  simple  plants 

§  188.   Runners 

§  189.    Stolons 

§  190.    Dissemination  or  spreading  of  the  plant  by 

propagation 

§  191.    Gemmae 

§  192.    Reproduction  by  spores 
§  193.    Reproduction  by  eggs 

§  194.    Fern  spores 

§  195.    Germination  of  spores 

§  190.    Another  form  or  generation  of  the  fern 

§  197.    Alternation  of  generations 

§  198.    The  two  generations  of  the  moss 

§  199.   Occurrence  of  generations  . 

§  200.    The  generations  of  seed  plants  . 

§  201.    The  gametophyte,  or  egg-bearing  generation  in  the 

plant         

§  202.    The  structure  of  a  flower    . 
§  203.   The  spores  of  seed  plants   . 

§  204.    Pollination 

§  205.    The  wind  as  an  aid  to  pollination 

§  206.   Animals  as  pollen  carriers 

§207.   Fertilization 


vegetative 


seed 


VIII.    Seeds  and  Fruits 


§  208.  The  seed 

§  209.  The  existence  of  the  seed  . 

§  210.  Fruits 

§  211.  The  cocoanut      .... 

§212.  The  date 

§  213.  Maize,  or  Indian  corn 

§  214.  The  fruit  of  the  clot-bur,  Xanthium 

§  215.  Xature  of  the  fruits  of  Xanthium 

§216.  The  apple 

§  217.  The  bean  and  pea 


XVI 


CONTENTS 


IX.    The  Power  or  Energy  of  the  Plant 

§  218.  Energy  of  the  plant 

§  219.  Sources  of  energy 

§  220.  Sunlight  as  a  source  of  energy  . 

§  221.  Chemical  compounds  as  a  source  of  energy 

§  222.  Physical  attraction  as  a  source  of  energy 

§  223.  Release  of  energy 

§  224.  Respiration,  or  breathing  .... 

§  225.  Changes  in  the  air  produced  by  breathing 

§  226.  Plants  by  day  and  by  night 

§  227.  Relation  of  the  living  world  and  the  atmosphere 

§  228.  Energy  of  physical  attraction     .... 

§  229.  Outward  work  accomplished  by  physical  attraction 


PAGE 

182 
182 
183 
183 
184 
184 
184 
185 
186 
187 
189 
190 


X.    Relations  of  Plants  to  Each  Other,  and  the 
Place  in  which  they  Live 


§  230.  Societies  and  communities 191 

§  231.  Plant  societies 192 

§  232.  Foundations  of  society 192 

§  233.  Communities  change 193 

§  234.  AVater  and  plants 194 

§  235.  Temperature  and  plants 194 

§  236.  The  soil  and  plants 195 

§  237.  Light  and  plants 195 

§  238.  Wind  and  plants 196 

§  239.  Forests        .         .         .         .         .         ...         .         .         .196 

§  240.  Relations  of  members  of  the  forest 201 

§  241.  Time  of  blooming 201 

§  242.  Seasonal  activity 202 

§  243.  Families  and  species  in  a  community        ....  204 

§  244.  Meadows 205 

§  245.  Rock  societies .        .206 

§  246.  Pond  societies 207 


CONTENTS  XVU 

PAGE 

§  247.  Locations  occupied  by  different  kinds  of  communities      .  209 

§  248.    Extermination  of  a  forest 210 

§249.   Fields 211 

§  250.    Course  of  further  study 211 

Index 213 


THE  NATUEE  AND  WOEK  OF  PLANTS 


I.    THE    COMPOSITION    AND    PURPOSES    OF 
PLANTS 

1.  The  plant  is  composed  of  living  matter. — The 
tints  of  a  flower,  the  graceful  curves  of  a  twining 
vine,  and  the  uncouth  forms  of  the  cactus  claim  our 
attention,  because  they  excite  our  curiosity  and 
admiration.  These  and  many  other  features  of  the 
vegetable  world  become  of  much  greater  interest, 
however,  when  it  is  learned  that  the  color  of  the 
rose,  the  lacelike  fronds  of  the  fern,  the  imposing 
trunk  of  the  forest  tree,  the  spines  of  the  thistle, 
and  the  juicy  sweetness  of  a  berry  are  all  due  to  the 
action  of  a  wonderful  substance,  which  is  known 
to  be  living,  and  is  usually  termed  protojjlasm.  If 
our  studies  are  extended,  we  may  learn  that  this  liv- 
ing substance  is  the  most  important  part  of  our 
bodies,  as  well  as  those  of  all  other  animals  and  of 


jj,  C.  StaU  Colw 


2  THE  NATURE  AND    WOBK  OF  PLANTS 

plants  also.  Still  further  it  would  be  found  that 
protoplasm  has  certain  ways  of  doing  things,  certain 
modes  of  action,  or  is  governed  by  a  number  of  laws, 
no  matter  whether  it  is  in  the  body  of  a  plant  or 
animal.  Very  little  is  known  of  the  composition  of 
protoplasm,  except  that  a  great  many  kinds  of 
material  are  used  in  its  construction,  and  that  these 
materials  are  blended  and  woven  together  in  a  very 
complex  and  intricate  manner.  Protoplasm  is  a  very 
delicate  and  sensitive  substance,  easily  destroyed  or 
injured,  hence  when  it  forms  the  body  of  a  phmt  or 
animal,  it  is  generally  necessary  for  it  to  construct 
masses  or  sheets  of  lifeless  substance,  which  it  fash- 
ions into  tools  for  the  performance  of  its  work,  or 
into  coverings  which  hide  it  from  sight  and  protect 
its  fragile  mechanism  from  damage  by  heat,  cold, 
dryness,  or  other  agencies  which  might  crush,  tear, 
or  injure  it  in  any  manner.  The  yellowish  masses 
of  slimy  substance  to  be  seen  on  decaying  logs  are 
the  bodies  of  a  slime  mould  which  is  composed  of 
naked  protoplasm.  This  organism  is  so  low  in  the 
scale  of  life  that  it  is  difficult  to  say  whether  it  is 
more  like  a  plant  or  an  animal,  and  it  forms  cover- 
ings for  its  protoplasm  in  the  reproductive  stage 
only. 


COMPOSITION  AND  PURPOSES   OF  PLANTS  3 

2.  The  purposes  of  plants.  —  Tlie  chief  purpose 
of  every  individual  plant  is  to  give  rise  to  other 
individuals  of  the  same  kind.  In  carrying  out  this 
purpose  the  protoplasm  strives  constantly  to  perfect 
itself,  or  rather  its  tools  and  organs,  and  to  adapt 
these  more  exactly  to  the  conditions  of  light,  mois- 
ture, temperature,  and  the  food  supply  under  which 
it  is  compelled  to  live.  The  manner  in  which  the 
living  substance  attempts  to  improve  its  own  mechan- 
ism and  the  usefulness  of  its  tools  determines  the 
form  and  structure  of  its  body,  and  accounts  largely 
for  the  differences  between  an  oak  tree  and  a  violet. 

3.  Great  differences  aynong  plants.  —  It  needs  but 
the  most  casual  glance  at  a  field  or  forest  to  find 
that  there  are  many  different  kinds  of  plants  in 
it.  Thus  it  is  easily  seen  that  some  are  grasses  form- 
ing a  thick  velvety  carpet  of  sod  on  the  surface  of 
the  soil,  while  others  are  trees  and  send  their  round 
trunks  a  hundred  feet  into  the  air.  The  differences 
between  the  grasses  and  the  trees  are  very  great,  but 
all  plants  are  not  so  much  unlike  as  these  two  groups. 
It  will  be  found  that  there  are  many  kinds  of  trees 
and  many  kinds  of  grasses.  Thus  to  one  familiar 
with  the  out-of-door  world,  the  maple  tree  is  not  to 


4  THE  NATURE  AND    WORK  OF  PLANTS 

be  confused  with  the  oak  or  beech,  or  the  walnut 
with  the  sycamore,  wliile  the  pine  and  poplar  are 
so  unlike  that  they  might  be  distinguished  even  at 
night.  In  the  same  manner  the  mosses  and  ferns 
comprise  many  forms.  The  simple  plants  which  float 
upon  the  surface  of  the  water  in  ponds  also  show 
various  colors,  shapes,  and  methods  of  forming 
colonies  in  evidence  that  they  do  not  all  live  alike. 

4.  The  oaks,  maples,  elms,  ferns,  mosses,  and  pond 
scums  are  not  all  of  the  same  kind  among  them- 
selves.  —  Now  if  one  goes  through  a  forest  and  looks 
carefully  at  all  of  the  maple  trees  he  may  see  in  a 
half  day's  walk,  he  will  find  that  they  do  not  all 
have  the  same  appearance. 

In  the  Middle  states  one  is  very  likely  to  see 
"sugar  maples"  (Acer  saccharum),  large  handsome 
trees,  over  a  hundred  feet  high,  many  of  them  with 
grayish  bark,  large  leaves,  flowers  greenish-yellow 
in  color,  appearing  at  the  same  time  as  the  leaves, 
and  the  trunk  is  very  full  of  a  sweetish  sap  in  the 
spring.  On  the  edges  of  swamps  and  in  the  low 
grounds  will  be  found  other  maple  trees,  with  the 
bark  of  the  twigs  quite  reddish  in  color,  leaves  with 
sharp-pointed  lobes  and  some  hahs  on  the  veins,  the 


COMPOSITION  AND  PURPOSES   OF  PLANTS  5 

flowers  yellowisli-red,  and  appearing  before  the  leaves 
in  the  spring.  The  leaves  show  the  most  brilliant 
colors  in  the  autumn.  This  is  the  red  maple  (Acer 
ruhrum),  and  the  sugar  maple  and  the  red  maple 
trees  each  constitute  a  species.  The  trees  of  each 
species  live  in  certain  kinds  of  places,  and  have 
distinct  forms  of  leaves,  twigs,  fruit,  and  flowers 
adapted  to  the  conditions  under  which  they  exist, 
and  these  organs  are  developed  at  such  season  in 
the  two  species  as  will  enable  each  to  do  its  w^ork 
in  the  best  manner. 

The  violets  are  among  the  earliest  spring  flowers, 
and  it  would  be  possible  in  a  great  many  localities  to 
find  some  with  white,  others  with  blue,  and  others 
with  yellow  flowers.  Dig  up  a  specimen  of  each  and 
lay  them  side  by  side  on  the  table  or  a  sheet  of 
paper.  Compare  the  roots,  stems,  leaves,  and  flowers, 
as  to  their  number,  where  attached,  form,  and  color. 

This  will  show  that  the  three  violets  have  developed 
their  organs  in  various  manners,  and  that  the  three 
are  members  of  tliree  different  species  of  the  violets. 

A  good  conception  of  the  difference  between  spe- 
cies may  be  gained  from  a  comparison  of  a  wild 
cherry  tree  with  those  in  any  orchard,  and  of  the 
slippery  elm  with  the  white  elm. 


6  THE  NATURE  AND    WORK  OF  PLANTS 

5.  A  sj^ecies.  —  In  an  examination  of  a  number  of 
sugar  maple  or  red  maple  trees  it  will  be  seen  that 
they  are  not  all  exactly  the  same  size,  shape,  and 
color,  but  that  the  red  maples  show  some  differences 
among  themselves.  In  the  same  manner  the  violets 
with  yellow  flowers  are  not  exactly  the  same  shape 
and  size  as  to  leaves  and  stems.  Still  the  yellow 
violet  plants  are  more  like  each  other  than  they  are 
like  the  blue  violets. 

We  are  now  ready  to  define  a  species,  and  can  say 
that  a  species  is  a  group  of  individuals  very  much 
alike  one  another,  but  unlike  the  individuals  of 
another  species.  Further,  if  the  seeds  of  the  yellow 
violet  are  planted,  they  will  germinate  and  form 
plants  which  are  like  those  from  which  the  seeds 
were  taken.  It  may  then  be  said  that  the  seeds  of 
any  species  reproduce  or  give  rise  to  the  same  kind 
of  specimens  as  those  which  bore  the  seed.  The  seeds 
of  blue  violets  always  produce  blue  violets,  those  of 
yellow  violets  always  produce  yellow  violets,  and  so 
on  through  the  whole  list  of  over  a  hundred  thou- 
sand species  of  plants  which  form  seeds.  The  groups 
of  individuals  which  represent  the  sjDecies  may  alter 
their  habits  and  general  appearance,  little  by  little, 
from  generation  to  generation,  until  in  the  course  of 


COMPOSITION  AND  PUEPOSES   OF  PLANTS  7 

a  grecit  many  years  individuals  are  produced  quite 
unlike  the  originals ;  yet  there  are  no  abrupt  changes 
or  jumps  from  one  form  to  another.  Thus,  for  in- 
stance, the  belief,  quite  common  in  some  farming 
communities,  that  wheat  can  be  converted  into 
"Chess,"  or  ''Cheat,"  is  founded  on  an  utter  impos- 
sibility. It  will  be  shown  later  (§  197)  that  plants 
have  two  generations,  or  two  forms  which  alternate 
with  each  other,  and  these  two  forms  are  quite 
prominent  in  the  mosses ;  but  in  such  cases  the  two 
forms  are  equally  invariable  and  may  not  be  changed 
quickly  or  suddenly. 

The  chief  point  of  interest  in  the  idea  of  a  species 
in  connection  with  the  work  to  be  followed  in  this 
book  is  the  fact  that  a  species  is  a  group  of  individu- 
als that  are  trying  to  adapt  themselves  to  a  certain 
mode  of  life  by  means  of  the  special  organs  in  the 
forms  of  stems,  leaves,  roots,  and  flowers  in  the 
higher  plants,  and  by  organs  which  do  the  same 
work  among  the  lower  forms.  And  furthermore, 
that  no  two  species  try  to  live  in  exactly  the  same 
manner. 

6.  Scope  of  ivorJc  described.  —  The  studies  de- 
scribed in  the  following  pages  make  up  an  outline 


8  THE  NATURE  AND    WORK  OF  PLANTS 

of  examination  of  the  plant  at  work,  and  consist  of 
observations  on  the  structure  of  the  organs  of  the 
plant  machine,  the  things  which  the  plant  may  do, 
the  way  in  which  it  secures  food,  avoids  injury,  and 
accomplishes  reproduction. 

An  attempt  will  be  made  to  determine  not  only 
the  kinds  of  work  a  plant  may  do,  but  in  some 
instances  the  opportunity  will  be  taken  to  measure 
the  amount  it  may  accomplish  in  the  same  manner 
that  the  capacity  of  an  engine  might  be  noted. 


II.     THE     MATERIAL    OF    WHICH     PLANTS 
ARE   MADE   UP 

7.  The  plant  is  an  engine. — The  plant  is  a 
machine,  and  is  composed  of  many  more  separate 
parts  than  a  watch  or  locomotive.  The  construc- 
tion of  a  watch  or  locomotive  may  be  learned  by 
tearing  one  to  pieces,  or  by  building  it  up  from  its 
separate  parts.  After  this  has  been  done  it  is  much 
easier  to  understand  the  action  of  these  machines. 
The  same  is  true  of  the  plant. 

The  composition  of  the  plant  might  be  found  by 
separating  it  into  its  different  substances,  after  the 
manner  of  the  chemist,  or  by  building  it  up  from  the 
materials  of  which  it  may  be  composed.  Neither  of 
these  methods  is  entirely  satisfactory  when  used 
alone,  because  they  cannot  be  completely  carried 
out.  The  substances  or  compounds  in  protoplasm  are 
so  delicate  that  when  we  seek  to  separate  them  they 
are  destroyed.  The  result  is  the  same  as  if  we 
attempted  to  tear  down  a  build hig  made  of  bricks 
so  fragile  that  they  would    crumble   at  the  touch ; 


10  THE  NATURE  AND    WORK  OF  PLANTS 

when  we  have  finished  we  have  nothing  but  a  pile 
of  rubbish  and  dust. 

Then,  again, .  we  cannot  actually  construct  proto- 
plasm with  our  own  hands;  but  we  may  ascertain 
the  substances  which  should  be  given  to  the  proto- 
plasm of  a  plant  in  the  form  of  food,  in  order  that  it 
should  be  able  to  grow  or  add  to  its  bulk.  While 
both  of  these  methods  are  subject  to  so  many  errors 
that  they  are  but  of  little  use  separately,  yet  both 
together  give  a  fan-  knowledge  of  the  composition  of 
the  bodies  of  plants. 

8.  Water,  charcoal,  and  ash.  —  Place  enough 
freshly  gathered  leaves  or  stems  to  make  about  half 
a  pound  in  a  small  tin  dish,  and  set  on  the  pan  of  a 
balance.  Weigh  carefully.  Now  place  the  pan  on 
the  top  of  a  stove  for  two  or  three  hours,  or  in  the 
hot  sunlight  for  twice  that  time.  Weigh  again. 
How  much  weight  has  been  lost  ?  Set  fire  to  the 
dried  material  and  attend  to  it  until  it  is  completely 
burned,  being  careful  that  none  of  the  ash  is  allowed 
to  escape  from  the  dish.  Now  weigh  again.  How 
much  weight  has  been  lost  this  time  ?  Clean  out 
the  pan  and  weigh.  Subtract  the  weight  of  the  dish 
from  the  figures  obtained  at  each  weighing  and  you 


THE  MATERIAL   OF  PLANTS  11 

will  have  first  the  weight  of  the  fresh  material, 
about  half  a  pound.  Wheu  the  fresh  plant  is 
dried,  it  needs  no  demonstration  to  show  that  water 
is  driven  off,  so  that  the  next  weight  represents 
the  material  in  the  plant  after  the  water  is  taken 
away.  This  dried  material  is  composed  of  two  dif- 
ferent kinds  of  substances.  When  it  is  burned, 
one  kind,  constituting  the  charcoal,  is  consumed, 
leaving  only  the  ash  or  mineral  substances  behind. 
If  these  weighings  are  carefully  made,  it  will  be 
found  that  the  water  makes  more  than  three-fourths 
of  a  growing  plant,  the  charcoal  generally  less 
than  one-fourth,  and  the  ash  only  one-fortieth  or 
one-fiftieth  of  the  total  weight.  The  ashes  that  col- 
lect in  a  stove  are  exactly  similar  to  those  obtained 
in  this  experiment,  of  course ;  and  it  is  well  known 
that  the  weight  of  the  ash  from  a  heavy  armful  of 
wood  is  very  small.  This  experiment  may  also  be 
carried  out  with  a  potato,  carrot,  or  turnip. 

The  relative  amounts  of  the  different  groups  of 
substances  vary  with  the  species  of  plants  exam- 
ined and  the  age  of  the  specimens.  The  greatest 
proportion  of  water  is  to  be  found  in  young  shoots, 
the  greatest  proportion  of  charcoal  in  old  woody 
stems,  and  the  greatest  proportion  of  ash  in  leaves. 


12  THE  NATURE  AND   WORK  OF  PLANTS 

This  last  fact  is  due  to  the  action  of  the  current  of 
water  which  constantly  travels  upward  through  the 
stem  into  the  leaves  where  it  evaporates  and  passes 
off  into  the  air,  leaving  behind  all  the  mineral  sub- 
stance brought  up  from  the  soil. 

9.  Leaves  shrink  in  drying.  —  During  the  drying 
process  the  loss  of  water  brings  the  particles  of 
which  the  plant  is  composed  closer  together,  and  it 
shrinks  in  size.  This  may  be  best  seen  in  leaves. 
Place  a  leaf  of  sunflower  or  some  fresh  rapidly  grow- 
ing leaf  on  a  sheet  of  paper,  and  trace  its  outline 
with  a  pencil.  Now  put  it  between  two  sheets  of 
blotting  paper  on  which  is  placed  a  weight  of  ten 
pounds.  Replace  the  blotting  paper  twice  a  day  for 
three  or  four  days.  Place  the  dried  leaf  over  the 
original  tracing,  and  make  a  second  drawing  of  its 
outline.  The  leaf  has  decreased  in  length  and  width. 
Measure  the  amount. 

10.  Mineral  coatings.  —  During  the  life  of  the 
plant  the  mineral  substances  in  it  are  usually  dis- 
solved in  water  and  are  not  visible.  In  some  in- 
stances, however,  these  minerals  take  the  form  of 
small  crystals  which  can  be  seen  Avith  the  micro- 
scope.    In  still  other  cases  the  mineral  is  deposited 


THE  MATERIAL   OF  PLANTS  13 

on  the  outside  of  the  plant  as  a  hard  covering 
easily  visible.  This  is  especially  true  of  the  scour- 
ing rush  (JEquisetum).  A  complete  coat  of  silicon 
covers  the  surface  of  the  stem  and  gives  a  rough 
feeling  when  handled.  The  mineral  sheath  is  so 
heavy  that  the  tissues  of  the  plant  may  be  de- 
stroyed and  it  will  remain  intact.  To  demonstrate 
this,  put  two  or  three  short  pieces  of  the  stem  of 
the  scouring  rush  into  a  dish  or  test  tube  and  cover 
with  a  mixture  of  three  parts  water  and  one  part 
hydrochloric  acid  (muriatic  acid).  Warm  the  prepa- 
ration nearly  to  the  boiling  point  for  two  hours. 
Pour  off  the  acid  and  wash  with  clean  water  two 
or  three  times.  The  beautiful  silicon  sheath  may 
now  be  handled  and  preserved  in  water  indefinitely. 
The  silicon  sheath  may  be  separated  in  a  still 
more  simple  manner  if  a  section  of  the  stem  is 
held  in  the  blaze  of  a  fire  or  the  flame  of  a  lamp. 
The  water  will  be  driven  off,  the  dried  material  will 
burn,  and  then  the  mineral  sheath  will  reach  a  red 
heat,  retaining  its  original  shape.  This  may  be 
preserved  dry  or  in  water. 

11.    Uses  of  mineral  coatings.  —  The  mineral  cover- 
ing of  the  scouring  rush  prevents  grazing  animals 


14  TUE  NATURE  AND    WORK  OF  PLANTS 

from  biting  the  stems,  althoiigli  it  is  not  known 
whether  they  were  formed  for  thcat  purpose  or  not. 
In  some  instances  mineral  substances  are  deposited 
on  the  bodies  of  plants  in  the  same  way  in  which 
they  are  accumulated  on  the  bottom  of  a  kettle  in 
which  water  is  boiled,  and  are  not  only  of  no  use 
to  the  plant,  but  are  a  detriment  to  growth  and 
food  formation. 

Certain  species  living  in  localities  where  there  is 
but  little  rainfall  and  where  the  air  is  very  dry, 
however,  have  a  layer  of  salts  on  the  surfaces  of 
the  leaves,  which  attracts  water  from  the  air,  thus 
preventing  these  useful  organs  from  drying  out. 
The  mineral  coating  of  a  stem  may  also  serve  a 
similar  purpose. 

12.  Aquatic  species  ivith  mineral  coatings.  —  Many 
plants  which  live  in  the  water  cause  the  mineral 
matter  dissolved  in  it  to  be  deposited  on  their 
surfaces.  This  may  be  seen  on  the  pond  weeds 
{Potamogetons),  if  specimens  are  taken  from  the 
water  and  allowed  to  dry.  Some  of  the  small 
threadlike  algae  are  said  to  be  "  calcareous  "  because 
they  are  found  surrounded  by  masses  of  lime  of 
greater  bulk  than  their  own  bodies.     Many  of   the 


TUE  MATERIAL   OF  PLANTS  15 

curious  rock  formations  in  the  Yellowstone  Park 
are  made  up  in  this  manner.  Some  of  the  powders 
used  to  polish  metals  are  taken  from  deposits  in 
the  soil,  and  they  consist  of  the  silicon  sheath  of 
minute  plants. 

13.  '^ Water  cultures''  ivith  and  ivithout  mmeral 
salts.  —  Fill  a  quart  fruit  jar  with  clean  rain  water, 
and  a  second  from  a  stream  or  pond.  Put  in  each 
a  freshly  cut  twig  of  willow  (Salix)  or  a  stem  of 
coleus,  and  place  both  in  sunlight  in  a  warm  room. 
Replace  the  water  weekly,  and  clean  out  the  jars. 
The  cuttings  will  soon  begin  to  grow  and  form 
leaves,  even  if  the  experiment  is  performed  in 
winter.  Compare  the  amount  of  growth  in  three 
or  four  weeks.  Have  they  grown  equally  ?  If  a 
difference  is  shown  in  the  number  and  size  of  the 
leaves  and  roots,  to  what  is  it  due  ?  The  follow- 
ing demonstration  may  throw  some  light  on  the 
subject. 

14.  Ash  or  mineral  salts  in  the  ivater  of  streams. 
—  Boil  a  quart  of  rain  water  in  a  dish  with  a  pol- 
ished inner  surface  until  the  liquid  has  all  disap- 
peared. Examine  the  bottom  of  the  dish.  Nothing 
has  been  left  behind,  and  rain  water  is  seen  to  be 


16  THE  NATURE  AND   WOBK  OF  PLANTS 

lacking   in   solid   matter  which   might   be   used   as 
food  by  the  plant. 

Now  boil  a  quart  of  water  from  a  stream  or 
pond  in  the  same  dish  until  it  has  all  passed  away 
in  the  form  of  vapor.  A  gray  coating  remains  on 
the  bottom  of  the  dish,  consisting  of  mineral  salts, 
which  may  be  taken  up  by  the  plant,  and  which 
forms  the  ash  when  it  is  burned.  This  is  identical 
with  the  "lime"  which  is  deposited  on  the  inside 
of  tea-kettles  in  which  hard  water  is  boiled. 

15.  Elements  found  in  plants.  —  If  a  complete 
chemical  analysis  were  made  of  the  plant,  it  would 
be  found  that  it  had  selected  sulj^hur,  pliosijhorus, 
magnesium,  calcium,  potassium,  sodium,  and  iron 
from  the  minerals  present  and  had  taken  these  up 
in  certain  proportions  most  useful  to  it.  Besides 
these,  it  also  gets  nitrogen,  chlorine,  carhon,  hydro- 
gen, and  oxygen  from  the  soil  and  air.  Many  species 
take  up  quantities  of  silicon,  as  did  the  scouring  rush. 
The  seaweeds  use  iodine  and  hromine,  and  still  other 
elements  are  taken  up  by  a  few  forms,  and  may 
or  may  not  serve  as  food.  Thus  many  of  the  grasses 
and  sedges  do  this,  and  some  of  them  use  the 
mineral  to  give  a  sharp  saw-toothed  edge  to  their 


THE  MATERIAL   OF  PLANTS  17 

leaves,  which  cut  like  knives  when  drawn  care- 
lessly through  the  hand.  This  device  may  well  be 
a  protection  against  animals,  for  they  will  not  only 
not  eat  such  plants,  but  avoid  walking  among  them. 

The  plant  may  pick  up  almost  any  salt  in  the  soil 
penetrated  by  its  roots,  of  even  such  poisonous  sub- 
stances as  zi7ic,  antimony,  arsenic,  or  cop^^e?'.  The 
wood  of  large  numbers  of  trees  growing  in  the 
regions  which  have  copper-bearing  rock  in  the  soil 
may  contain  as  much  as  one  per  cent  of  their  dry 
weight  in  copper,  although  this  metal  is  of  no  use  to 
the  plant  and  is  slightly  poisonous  to  it.  The  same 
is  true  in  regard  to  zinc  and  arsenic.  In  general,  it 
may  be  said  that  no  substance  is  taken  up  in  great 
proportion  unless  used  as  food. 

Animals,  especially  man,  take  in  substances  in 
food  which  do  not  actually  enter  into  the  tissues  of 
the  body,  but  promote  the  digestion  and  use  of  the 
necessary  elements.  The  same  will  apply  in  some 
degree  to  plants.  It  is  necessary  for  the  proper 
absorption  and  use  of  the  indispensable  food  sub- 
stances that  others  should  be  present  with  them 
which  are  not  used.  Thus  the  plant  does  not  use 
sodium  in  constructing  protoplasm,  yet  it  should 
have  this  substance  in  its  food  solutions. 


18  THE  NATURE  AND    WORK  OF  PLANTS 

16.  Substances  servi7ig  as  food.  —  A  fairly  perfect 
food  for  the  plants  in  the  water  culture  experi- 
ment described  in  §  13  may  be  made  by  adding  to 
each  quart  of  rain  water  put  into  the  jars  ten  grains 
each  of  common  salt,  plaster  of  Paris,  Uj^som  salts, 
calcium  j^^iosjjJiate,  and  a  few  drops  of  iron  chloride. 
It  will  be  noted  that  common  salt  is  a  compound  of 
sodium  and  cidorine.  The  sodium  does  not  actually 
enter  into  the  body  of  the  plant,  yet  its  presence  in 
the  food  is  quite  useful. 

17.  Compounds  in  the  plants.  —  The  different  sub- 
stances taken  up  by  the  plant  consist  of  twelve 
or  thirteen  elements,  and  these  are  united  again  in 
such  manner  as  to  form  many  hundreds  of  different 
compounds.  The  formation  of  these  compounds  is 
generally  for  some  specific  purpose.  Thus  sugar  is 
built  up  from  the  carbon,  hydrogen,  and  oxygen  taken 
from  the  food  substances,  and  it  is  used  in  the  con- 
struction of  living  matter,  kept  as  a  reserve  material, 
or  it  may  be  sent  from  one  part  of  the  body  of  the 
plant  to  another.  Acids  are  formed  for  many  pur- 
poses, celhdose  for  cell  walls  and  coverings  for  the 
protoplasm,  p)roteins  to  build  up  the  living  substance 
itself,  which  is  constantly  wearing  out. 


TUB  MATERIAL   OF  PLANTS  19 

18.  7'esis  for  the  contents  of  the  plant.  —  If  a  raw 
potato  is  crushed  in  clear  water,  the  latter  becomes 
milky,  and  by  placing  some  of  it  in  a  small  glass 
and  holding  up  to  the  window,  numbers  of  minute 
granules  may  be  seen.  They  are  not  more  than  a 
hundredth  of  an  inch  in  diameter.  If  a  few  drops 
of  a  tincture  of  iodine  obtained  from  a  druggist  is 
added  to  the  water,  it  turns  blue,  owing  to  the 
action  of  iodine  upon  starch.  Put  a  drop  of  the  tinc- 
ture on  the  cut  surface  of  the  potato  and  note  the 
result. 

Apply  iodine  to  the  cut  surfaces  of  stems  and  roots, 
and  determine  the  portions  in  which  starch  may  be 
found. 

Sugar  in  sugar-cane,  sorghum,  fruits,  or  the  sugar 
beet,  or  in  the  sap  of  the  maple,  may  be  detected  by 
the  taste,  and  the  sour  acids  may  be  found  in  the 
same  manner. 

If  you  were  to  take  the  plant  to  a  chemical  labora- 
tory, and  make  a  complete  chemical  analysis  of  it,  a 
large  number  of  other  substances  would  be  found, 
such  as  oils,  tannins,  alkaloids,  j^^oteins,  mineral 
salts,  etc. 

Animals,  including  man,  have  found  uses  for  many 
of  these  substances,  and  species  which  produce  them 


20  THE  NATURE  AND    WORK  OF  PLANTS 

are  grown  or  cultivated  in  great  numbers.  It  is  to 
be  borne  in  mind  that  the  species  was  not  devel- 
oped for  the  purpose  of  being  useful  to  anything 
except  itself.  Man  has  learned  to  take  advantage 
of  the  capacity  of  the  plant  for  forming  certain 
substances,  and  cultivates  these  species  in  order  to 
get  their  products.  This  intelligent  action  is  shared 
by  certain  lower  animals  which  cultivate  crops  of 
moulds  and  use  them  for  food. 


III.  THE  MANNER  IN  WHICH  DIFFERENT 
KINDS  OF  WORK  ARE  DIVIDED  AMONG 
THE   MEMBERS   OF  THE   BODY 

19.  Kinds  of  work,  or  fimctio7is  of  the  plant.  — 
In  accomplishing  the  purpose  of  its  existence  a  plant 
is  compelled  to  do  a  large  number  of  different  things, 
or  carry  on  a  variety  of  processes.  Chief  among 
these  are  the  absorption  of  material  from  which  food 
is  to  be  formed  from  the  soil  and  air ;  the  conversion 
of  these  substances  into  compounds  suitable  for  stor- 
age, transportation,  or  use  by  the  protoplasm ;  the 
assimilation  of  the  food  into  the  living  substance, 
huilding  up  and  enlarging  its  bod}^,  storing  up  surplus 
food  for  future  use,  conducting  water  and  other  mate- 
rial from  one  part  of  its  body  to  another,  digesting 
the  reserve  material,  such  as  starch,  when  needed  for 
food,  hreathing,  throiving  aivay  the  worn-out  and 
useless  material,  liolding  the  body  in  the  proper  posi- 
tion, and  finally,  and  most  important  of  all,  taking 
care  that  the  species  is  preserved  by  giving  rise  to 
new  individuals  by  means  of   spores,  seeds,  imnners, 

21 


22  THE  NATURE  AND   WORK  OF  PLANTS 

offsets,  and  other  structures  necessary  for  the  process. 
In  addition,  the  plant  must  use  a  large  amount  of 
energy  and  material  in  j^^otecting  all  of  its  parts 
from  injury  or  destruction  by  the  climate,  other 
plants,  or  by  animals. 

20.  Organs.  —  In  the  lower  or  simpler  plants, 
such  as  algse  and  bacteria,  all  of  these  different 
things  or  functions  are  carried  on  by  a  very  small 
body,  often  consisting  of  a  single  cell  that  could  not 
be  seen  by  the  unaided  eye.  The  whole  body  is  used 
in  carrying  on  nearly  all  of  the  various  kinds  of 
work.  The  "  higher  "  plants  are  those  which  have 
developed  separate  portions  of  their  bodies,  especially 
suited  to  one  or  a  few  kinds  of  work.  The  part  of 
a  plant  thus  devoted  to  one  or  to  a  group  oi  functions 
is  termed  an  organ.  Thus  the  root,  stem,  leaf,  and 
flower  are  each  responsible  for  certain  kinds  of  work 
necessary  for  the  welfare  of  the  plant,  and  they  are 
the  principal  organs  of  the  higher  plants. 

21.  Tissues.  —  If  the  structure  of  any  of  the 
organs  is  examined,  it  will  be  found  that  it  is  made 
up  of  a  number  of  different  kinds  of  material.  Thus 
in  an  elder  stem  may  be  found  pith,  ivood,  cambium, 
and  lark.     The  different  masses  are  made  up  of  dif- 


THE  DIVISION  OF   WORK  23 

ferent  kinds  of  cells,  and  are  called  tissues.  Every 
tissue  has  a  special  share  in  the  work  of  the  organ 
in  which  it  occurs.  The  tendency  of  protoplasm  to 
divide  its  work  among  separate  organs  is  one  which 
allows  the  living  matter  to  carry  on  all  of  its 
functions  most  economically  and  efficiently,  and  it 
has  been  the  chief  principle  in  the  development  and 
evolution  of  all  living  things. 

22.  Method  of  study  of  functions  and  organs. — 
It  will  be  found  most  convenient  to  take  each  organ 
of  the  higher  plants  and  learn  what  we  may  con- 
cerning the  w^ork  it  does  and  the  way  in  which  it  is 
done.  After  a  fair  conception  of  the  nature  of  the 
activities  of  the  plant  has  been  gained  in  this  man- 
ner, it  will  be  possible  to  understand  much  more 
clearly  the  mode  of  life  of  the  simpler  organisms  in 
which  many  kinds  of  work  are  carried  on  by  the 
same  tissues  or  even  by  the  same  cell. 

An  insight  of  the  special  capacities  of  the  separate 
organs  will  also  enable  one  to  understand  the  w^ork 
in  which  the  entire  body  of  a  higher  plant  par- 
ticipates. 


IV.   THE   ROOTS 

23.  Functions  of  the  roots.  —  The  higher  plants 
are  generally  stationary,  and  do  not  move  around 
except  in  the  case  of  aquatics  which  float  from  place 
to  place  in  currents  of  water.  It  was  found  in 
previous  experiments  that  water  which  washed  the 
soil  in  streams  contains  certain  salts  which  it  has 
extracted  from  the  soil,  and  that  these  salts  are  nec- 
essary to  make  up  the  food  of  the  plant.  Further- 
more, it  will  be  seen  by  an  examination  of  a  few 
specimens  that  the  roots  are  the  organs  which  pene- 
trate the  soil  to  any  depth,  holding  the  plant  in  its 
place,  and  it  is  through  these  organs  that  food  salts 
might  be  taken  up.  The  root  then  may  be  credited 
with  two  kinds  of  work :  fixation  or  anchorage,  and 
absorption  of  food. 

24.  Roots  hold  the  stem  firmly  in  positioii.  — 
Grasp  the  stem  of  a  sunflower,  or  geranium,  or  some 
small  plant,  and  attempt  to  pull  it  from  the  ground. 
A  great  amount  of  force  will  be  necessary,  as  one 

24 


v.  estate  Collets 


THE  ROOTS  25 

may  easily  learn  in  "  weeding "  a  flower  or  garden 
bed.  Try  to  uproot  another  specimen  by  pulling 
sidewise  on  the  stem,  and  it  will  be  found  even  more 
difficult  to  accomplish.  Now  tie  a  strong  cord 
around  the  stem  of  a  third  specimen,  and  pass  the 
cord  over  a  thick  branch  of  a  tree  or  the  top  of  a 
fence.  Tie  weights  or  heavy  objects  to  the  free 
end  of  the  cord,  and  add  to  them  until  the  plant 
is  torn  from  the  ground.  How  many  pounds  were 
necessary  to  do  this  ?  If  a  strong  pair  of  spring 
scales  are  at  hand,  this  experiment  may  be  per- 
formed more  exactly.  Tie  the  hook  of  the  instru- 
ment to  the  upper  part  of  the  stem  of  a  tomato 
or  other  small  plant,  and  pull  directly  upward.  Note 
the  number  of  pounds  indicated  by  the  scale  as  the 
plant  is  torn  loose.  The  plant  is  seen  to  come  away 
with  a  mass  of  earth  adhering  to  the  roots.  The 
roots  are  very  plainly  organs  of  fixation,  and  not 
only  penetrate  the  soil,  but  clamp  a  large  mass  so 
that  they  may  not  be  easily  torn  up.  These  organs 
anchor  stems  so  securely  that  very  heavy  action  of 
wind,  water,  or  of  animals  is  necessary  to  displace 
them.  In  a  walk  through  a  forest  in  which  trees 
have  been  uprooted  by  storms,  note  the  manner 
in  which  the  masses  of  earth  are   clamped  by  the 


26  THE  NATURE  AND    WORK  OF  PLANTS 

large  roots  and«the  general  shape  of  the  root  system. 
What  kinds  of  trees  are  most  easily  blown  over? 

25.  Boots  loere  first  developed  for  fixation.  —  In 
the  development  of  the  plant  world,  roots  were 
first  formed  by  the  protoplasm  for  the  purpose  of 
holding  the  organism  in  place,  and  in  some  of  the 
simpler  forms  of  plants  there  are  to  be  seen  species 
in  which  these  organs  serve  no  other  purpose.  The 
ribbonlike  bodies  of  the  marine  seaweeds,  the  lami- 
narias  which  may  be  a  foot,  or  several  hundred  feet, 
in  length,  are  fastened  to  the  rocks  by  a  system  of 
"  holdfasts,"  not  much  larger  than  the  hand.  The 
great  extension  of  root  systems  to  be  seen  in  plants 
growing  in  the  soil  is  chiefly  for  the  purpose  of 
absorption.  If  the  root  system  of  such  a  species  is 
carefully  dug  up,  it  will  be  found  to  penetrate  the 
soil  to  a  depth  of  a  few  feet,  and  to  extend  out  sev- 
eral feet  from  the  base  of  the  stem.  Indeed,  the 
total  length  of  the  root  system  generally  exceeds 
that  of  the  stems  and  branches.  It  has  been  found 
by  actual  measurement  that  the  roots  of  a  sun- 
flower placed  end  to  end  would  reach  a  distance 
of  hundreds,  and  those  of  a  squash  thousands,  of 
feet. 


THE  ROOTS  27 

26.  Shrinkage  of  roots  to  aid  in  fixation.  —  Ex- 
amine the  full-grown  roots  of  a  hyacinth  {Hya- 
cinthus),  calla,  or  jack-in-the-pulpit  (Arismma).  A 
short  distance  back  of  the  tip  the  surface  appears  to 
be  wrinkled.  The  wrinkling  is  due  to  the  fact  that 
the  root  elongates  by  growth  at  the  tip,  and  as  soon 
as  any  portion  reaches  a  certain  age,  it  shortens  and 
causes  little  folds  to  appear  on  the  surface  tissue,  or 
epidermis.  If  India-ink  marks  are  placed  on  young 
roots,  and  the  distance  between  them  measured  be- 
fore and  after  wrinkling,  it  will  be  found  that  some 
shrink  one-tenth  or  even  one-fifth  of  their  whole 
length.  If  the  shrinkage  of  the  root  simply  pulled 
it  through  the  soil,  it  could  be  of  no  benefit  to  the 
plant  and  might  work  damage.  The  tip  of  the  root, 
however,  is  firmly  attached  by  means  of  the  root- 
hairs,  and  then  this  portion  is  bent  around  so  many 
small  rocks  that  it  is  not  easily  pulled  back  by  the 
contraction.  As  a  result,  the  base  or  upper  end  of 
the  root  with  the  stem  to  which  it  is  attached  is 
pulled  down  into  the  soil  still  more  firmly.  Further- 
more, if  the  root  has  sent  out  side  branches,  the  soil 
between  the  side  branches  will  be  clamped  between 
them  in  a  manner  well  illustrated  by  the  masses  of 
rock  and  dirt    seen   adhering  to   the  roots  of  pros- 


28  THE  NATURE  AND    WORK  OF  PLANTS 

trated  trees.  The  side  roots  contract  in  the  same 
manner  so  that  the  entire  root  system  is  a  great  com- 
plex clamp  which  grasps  the  soil  and  rocks  very 
firmly,  and  thus  greatly  increases  the  anchoring 
power  of  the  underground  organs. 

27.  The  structure  of  the  root.  —  Examine  an  old 
root  that  has  begun  to  decay.  Material  from  a 
hyacinth  or  calla  will  be  suitable.  Hold  the  large 
end  in  one  hand  and  strip  off  the  outer  delicate  tis- 
sue, when  a  central  cord  or  fibrous  mass  will  be  seen. 
When  the  organ  is  growing  rapidly  the  outer  cylin- 
der of  soft  tissue  absorbs  water  and  expands,  stretch- 
ing the  central  fibrous  cord  as  one  might  a  rubber 
string.  When  the  root  grows  old  the  outer  tissues 
change  their  form,  allowing  the  central  cord  to 
shorten,  and  wrinkling  the  epidermis  in  the  process. 

28.  Climhing  roots. — A  large  number  of  species 
of  the  higher  plants  form  long  slender  stems  which 
are  unable  to  stand  upright,  and  which  are  specially 
adapted  for  attachment  to  the  trunks  of  trees  and 
6ther  tall  objects,  to  which  they  are  fastened  by 
various  methods.  In  many  instances  roots  are  de- 
veloped many  feet  above  the  ground,  and  these 
adhere  to  the  tree  in  various  ways,  holding  the  stem 


THE  BOOTS  29 

securely  in  place.  Here  the  original  function  of  fixa- 
tion alone  is  carried  on,  since  generally  no  opportu- 
nity is  offered  to  absorb  food.  So  finely  are  these 
roots  adapted  for  anchorage  in  difficult  places  that 
they  can  secure  a  foothold  on  the  polished  surface  of 
a  marble  column  or  a  sheet  of  glass.  This  may  be 
seen  in  the  ivy  of  the  gardeners  {Ficus). 

29.  Stilt  7Vots. — A  special  adaptation  of  the 
fixative  function  is  to  be  seen  in  the  roots  which 
start  from  the  stem  a  short  distance  above  the 
ground  and  extend  outwardly  and  downwardly  until 
they  enter  the  soil  several  inches  perhaps  from  the 
main  stem.  Such  roots  brace  the  stem,  and  if  the 
tips  form  branches  after  entering  the  soil,  their  effi- 
ciency is  still  further  increased.  This  may  be  seen 
in  the  wheat,  corn,  and  other  grasses,  as  well  as  in 
the  palms  and  the  mangroves.  Go  into  a  cornfield 
in  early  autumn  and  note  the  stilt  roots.  Pull  a 
stalk  sidewise  and  note  their  action. 

30.  Columnar  7^oots.  —  In  many  of  the  forest 
trees,  such  as  the  beech,  large  roots  are  formed  at 
the  surface  which  take  the  form  of  an  upright  thick 
sheet  of  wood  tapering  in  width  toward  the  outer 
end   where    it    is  covered   by  the   soil.     These  also 


30  THE  NATURE  AND    WORK  OF  PLANTS 

serve  the  purpose  of  bracing  the  stem  against  being 
blown  over. 

31.  Keel  or  hallast  roots.  —  Some  aquatic  plants 
are  in  the  form  of  a  leaflike  stem  or  a  rosette  of 
leaves  which  floats  on  the  surface  of  the  water,  and 
one  or  more  roots  are  formed  which  hang  downward 
in  the  water,  serving  to  keep  the  floating  parts  in 
proper  position,  and  perhaps  also  as  organs  of  absorp- 
tion. The  members  of  the  duckweed  family  (Lenma) 
and  the  water  hyacinth  are  good  examples  of  this, 
and  should  be  examined. 

32.  Substances  of  ivhich  the  soil  is  comjyosed. — 
Examine  a  half  cupful  of  soil  taken  from  the  gar- 
den, by  means  of  a  hand  lens,  or  spread  it  out  on  a 
sheet  of  glass  and  hold  in  direct  light.  When  sepa- 
rated into  small  portions  with  a  needle  it  may  be 
seen  to  be  made  u]3  of  irregular  bodies  of  various 
sizes,  bits  of  rock,  fragments  of  leaves,  stems,  seed 
coats,  splinters  of  bone,  feathers,  cast-off  shards  of 
beetles,  as  well  as  a  variety  of  other  matter  which 
will  depend  on  the  locality  from  which  the  soil  was 
taken.  Every  particle  has  a  faint  shiny  appearance 
which  disappears  more  or  less  completely  if  the  mass 
is  dried  over  a  hot  stove.     The  shiny  appearance  was 


THE  BOOTS  31 

due  to  a  tliin  layer  of  water  which  surrounded  eacli 
particle.  It  is  this  thin  layer  of  water  which  is 
taken  up  by  the  plant,  and  it  contains  the  mineral 
salts  of  the  soil  in  solution. 

33.  The  soil  and  root-hairs  adhere.  —  If  the  speci- 
mens which  were  torn  up  were  examined,  it  would 
have  been  seen,  that  in  addition  to  the  masses  of 
soil  clamped  by  the  roots,  there  was  a  thin  layer 
immediately  surrounding  each  separate  root  which 
did  not  come  away  easily.  Pull  up  a  young  bean 
plant  or  any  other  that  may  be  convenient,  and 
examine  the  roots  with  a  hand  lens.  The  minute 
particles  of  soil  are  seen  to  be  adherent  to  small 
glistening  hairs  w^iich  arise  from  the  root,  rather 
than   to  the   surface  of  the  root  itself. 

34.  Boot-hairs  and  the  region  from  ivhich  they 
arise.  —  The  root-hairs  are  very  delicate  in  structure, 
and  it  may  be  seen  very  readily  that  they  are  not 
foimd  along  the  entire  extent  of  the  root.  A  better 
view  of  these  organs  may  be  seen  if  some  are  grown 
where  they  may  not  adhere  to  any  solid  particles 
which  partially  hide  them.  To  do  this,  cut  a  cir- 
cular piece  of  blotting-paper  the  size  of  the  bottom  of 
a  plate,  soak  it  in  water,  and  lay  it  in  a  plate.     Drop 


32  THE  NATURE  AND   WORK  OF  PLANTS 

a  dozen  seeds  of  wheat  or  oats  or  radish  on  the  blot- 
ting-paper and  cover  with  a  glass  dish.  After  ger- 
mination has  proceeded  for  two  or  three  days,  take 
up  one  of  the  seedlings  and  hold  between  the  win- 
dow and  the  eye.  Innumerable  fine  hairs  are  seen 
projecting  from  the  roots  on  all  sides.  If  these 
were  examined  with  a  hand  lens,  they  would  be  seen 
to  be  small  tubes.  Compare  the  number  of  root- 
hairs  near  the  tip  with  those  of  the  basal  portion  of 
the  root :  where  are  they  most  plentiful  ?  The  tubes 
are  the  shape  of  a  finger  of  a  glove,  and  when  thrust 
in  among  the  hard  particles  of  the  soil  they  take 
irregular  shapes  and  adhere  very  closely  to  the  bodies 
they  touch,  as  may  be  seen  if  a  thin  layer  of  sand 
is  placed  on  the  paper  at  the  beginning  of  the 
experiment. 

35.  Action  of  roots  which  have  heen  deprived  of 
hairs,  —  Perhaps  the  best  method  of  illustration  of 
the  uses  of  root-hairs  is  to  note  the  action  of  a 
root  from  which  they  have  been  taken.  To  do  this 
remove  a  young  sunflower  plant  from  the  ground 
and  shake  and  brush  all  of  the  soil  from  the  roots. 
This  will  carry  off  all  the  root-hairs,  but  if  per- 
formed carefully,  will  not  otherwise  injure  the  roots. 


THE  BOOTS  33 

Replace  the  plant  in  the  soil  as  it  was  before.  It 
will  be  seen  to  wilt,  no  matter  how  much  water  is 
poured  over  it.  From  this  it  is  fair  to  conclude 
that  a  root  from  which  the  hairs  have  been  broken 
cannot  absorb  enough  water  to  meet  the  needs  of 
all  the  leaves  and  stems. 

The  root-hairs  serve  the  general  purpose  of  in- 
creasing the  amount  of  absorbing  surface  of  the 
root,  and  as  a  general  rule  they  are  most  plentiful 
on  the  roots  of  species  growing  in  dry  soils,  and 
are  almost  wholly  absent  from  species  growing  in 
wet  soils,  swamps,  or  in  the  water. 

36.  Cmi  ivater  he  taken  in  through  the  leaves?  — 
Plants  which  are  slightly  wilted  often  revive  when 
the  leaves  are  sprinkled.  The  wetting  of  the  leaves 
might  be  of  benefit  to  the  plant  in  two  ways :  it 
might  prevent  them  from  drying  out  by  losing  the 
small  supply  of  water  they  are  receiving  from  the 
roots,  or  it  might  allow  them  to  absorb  water  like 
the  roots.  It  is  popularly  supposed  that  leaves  may 
take  up  water,  and  the  following  test  will  throw 
some  light  on  the  matter.  Place  a  young  potted 
specimen  of  geranium  or  tomato  where  it  may  not 
receive  water  until  it  has  wilted  from  thirst.     In- 


34  THE  NATURE  AND    WOEE   OF  PLANTS 

vert  the  pot,  and  sprinkle  the  leaves  with  water 
four  or  five  times  in  an  hour.  Does  it  recover 
from  wilting  ?  Place  the  plant  upright  and  water 
soil  copiously :  note  result.  Repeat  the  test  with 
other  plants  and  determine  the  matter  fully.  Can 
a  plant  absorb  water  from  the  air  in  sufficient 
quantity  for  its  needs  through  its  leaves? 

Still  another  method  for  testing  the  capacity  of 
the  leaf  for  absorbing  water  consists  in  floating  a 
wilted  leaf  of  the  fuchsia  or  begonia  in  a  vessel 
of  water,  with  the  upper  surface  downward,  and 
noting  results. 

37.  The  manner  in  ivJiich  7^oot-hairs  take  up 
liquids.  —  If  you  were  to  place  some  water  on  one 
side  of  a  piece  of  wet  parchment,  and  some  sugar 
on  the  opposite  side,  it  would  be  seen  that  the 
water  would  go  through  the  parchment  to  the 
sugar  in  a  very  short  time.  It  is  by  a  similar 
action  that  root-hairs  take  water  from  the  soil. 
The  root-hair  has  the  form  of  the  finger  of  a  glove 
with  the  walls  made  of  parchment.  It  is  lined 
with  living  matter,  and  is  filled  with  water  contain- 
ing; sus^ar  and  acids.  When  the  hair  touches  the 
thin  film  of  water  surrounding  the  particles  of   soil 


THE  ROOTS  35 

the  soil  water  is  drawn  through  the  walls  into  the 
cavity  in  the  same  manner  as  through  the  parch- 
ment. Besides  this  attractive  power  of  the  solution 
inside  the  root-hair,  the  thin  layer  of  living  matter 
lining  the  wall  is  of  such  nature  that  it  attracts 
water,  and  it  will  allow  the  passage  of  soil  water 
containing  mineral  substances ;  but  will  not  permit 
the  escape  of  any  of  the  liquid  containing  sugar, 
except  in  the  most  minute  quantities.  The  small 
amount  of  acid  which  does  escape  is  seen  to  act 
very  strongly  on  the  rocks  in  the  soil  (§  40). 

38.  Action  of  sugar.  —  The  manner  in  which 
sugar  draws  water  into  the  root-hair  is  illustrated 
by  the  following  method :  Cut  away  the  top  of  a 
carrot,  and  dig  out  a  cavity  as  large  as  an  acorn. 
Fill  the  cavity  with  dry  sugar  and  set  aside  for  a 
few  hours.  The  sugar  will  be  converted  into  sirup, 
having  drawn  water  through  the  walls  of  the  cells 
of  the  carrot. 

39.  Another  method  of  imitation  of  the  action  of 
root-hairs.  —  Select  a  long,  sound  potato,  and  bore 
a  cavity  in  it  reaching  from  one  end  nearly  to  the 
other,  being  careful  not  to  split  it.  Trim  the  skin 
from  the  closed  end  and  shape  it  so  that  it  will  stand 


36  THE  NATUBE  AND   WOBK  OF  PLANTS 

upright  in  a  saucer  of  water  an  inch  deep.  Fill 
the  cavity  with  sugar.  Examine  five  or  six  hours 
later.  The  sugar  will  have  drawn  the  soil  water 
from  the  saucer  through  the  wall  and  filled  up  the 
cavity  perhaps  to  overflowing  in  a  very  close  imita- 
tion of  the  action  of  a  root-hair. 

40.  Action  of  root-hah^s  on  particles  of  mineral 
substance.  —  The  root-hairs  take  up  the  thin  film  of 
water  surrounding  each  particle  of  soil,  and  as  the 
walls  of  the  hair  are  constantly  satm^ated  with  acid 
or  other  substances  which  will  corrode  rock,  they 
also  dissolve  some  of  it  in  such  manner  that  it  can 
be  absorbed.  To  demonstrate  this  action  fill  a  small 
flower-pot  half  full  of  common  garden  loam,  and  on 
top  of  it  lay  a  piece  of  marble,  an  oyster  or  clam 
shell  with  a  polished  surface  uppermost.  Cover  with 
three  inches  of  clean  sand.  Place  one  or  two  beans 
in  the  sand,  and  water  from  day  to  day.  After  a 
few  days  the  seeds  germinate  and  send  down  roots 
through  the  soil,  which  come  in  contact  with  the 
marble  or  the  shells.  Two  weeks  later  remove  the 
marble  or  shell,  wash  clean,  wipe,  and  allow  to  dry. 
Hold  between  the  eye  and  a  window  in  such  manner 
that   the  surface  will    be  seen  by  a  reflected   light. 


THE  BOOTS  37 

Irregular  branching  lines  or  roughened  areas  will 
show  where  the  roots  have  touched  the  polished 
surface,  and  the  hairs  have  etched  away  the  niineral. 

41.  TJie  fate  of  the  2^(^'^iic^6s  of  the  soil. — The 
particles  of  soil  may  be  roughly  classed  as  onineral 
and  organic.  The  latter  comprise  the  remains  of 
plants  and  animals  as  described  above,  and  constitute 
what  is  known  as  humus.  The  humus  is  constantly 
being  broken  down  by  the  action  of  the  soil  bacteria 
and  other  minute  organisms.  This  action  of  the 
bacteria  is  to  obtain  the  material  necessary  for  their 
own  food,  and  in  the  process  great  quantities  of  sub- 
stance are  formed  which  the  higher  plants  use.  The 
deep  layer  of  decaying  leaves  and  twigs  in  a  forest 
that  has  not  been  burned,  or  laid  bare  by  grazing 
animals,  is  a  good  example  of  humus  formation. 

The  mineral  particles  may  not  be  said  to  decay, 
but  they  are  constantly  being  broken  up.  The  water 
in  the  soil  always  contains  carhonic  acid  set  free  by 
living  plants  and  by  the  action  of  bactei^ia  on  the 
humus,  as  well  as  by  the  decomposition  of  certain 
minerals  themselves.  Other  acids  are  found  in  the 
air  and  are  washed  down  into  the  soil  by  rains.  The 
thin  film  of  water  which  surrounds  each  particle  con- 


38  THE  NATURE  AND    WORK   OF  PLANTS 

tains  these  acids,  and  slowly  eats  away  the  outer 
layers,  and  wherever  the  roots  or  their  hairs  touch, 
the  corrosion  is  increased  so  that  each  small  particle 
in  time  is  entirely  dissolved.  The  rock  particles 
would  thus  soon  disappear  from  the  soil,  but  frag- 
ments are  constantly  being  split  from  the  larger 
rocks  by  the  action  of  frost,  and  heat,  and  the  rend- 
ing action  of  large  roots,  so  that  the  supply  is  kept  up. 

42.  Food  material  in  the  soil  and  lioio  the  j^lctnt 
finds  it.  —  The  substances  which  are  formed  by  the 
corrosion  of  the  rocks  and  the  decay  of  humus  are 
not  found  everywhere  in  the  same  quantity,  but  are 
scattered  more  or  less  unevenly  through  the  soil. 
To  be  of  the  greatest  service  to  the  plant,  therefore, 
the  roots  must  not  only  absorb  substances,  but 
should  be  able  to  find  the  places  where  they  are 
most  abundant.  The  roots  of  the  higher  plants  are 
capable  of  doing  this,  and  direct  their  tips  into  the 
places  which  contain  the  food  and  w^ater  necessary 
for  the  plant.  In  order  to  be  able  to  accomplish  this, 
these  organs  have  become  sensitive  to  gravity,  light, 
heat,  moisture,  and  chemical  substances.  Some  of 
the  forms  of  sensitiveness  of  the  root  may  be  easily 
observed. 


THE  ROOTS  39 

43.  The  tijjs  of  primary  or  main  roots  point 
downivard.  —  Germinate  some  peas  or  beans,  as  in 
§  34,  and  when  the  first  roots  are  two  or  three 
inches  in  length,  thrust  a  pin  through  the  seeds  and 
fasten  to  a  piece  of  wood  or  cork  with  the  tips 
pointing  directly  upward.  Float  the  cork  or  wood 
in  a  saucer  of  water  and  cover  with  an  inverted 
tumbler.  Examine  two  to  four  hours  later.  The 
tip  will  generally  be  found  to  be  pointing  downward, 
having  curved  near  the  apex.  This  behavior  is  due 
to  its  sensitiveness  to  gravity.  The  root  tends  to 
place  its  axis  in  a  position  in  which  the  tip  is 
directed  toward  the  centre  of  the  earth.  This  move- 
ment is  not  caused  by  the  weight  of  the  root,  and  it 
does  not  bend  like  a  piece  of  soft  wax,  as  may  be  seen 
if  you  attempt  to  bend  it  back  to  its  original  posi- 
tion. It  breaks  in  consequence  of  such  forcible  bend- 
ing. The  curvature  of  the  root  is  due  to  the  action 
of  certain  definite  parts  designed  to  do  such  work. 

44.  The  tijjs  of  branches  of  the  main  roots  are 
directed  hoinzontally.  —  The  downward  growth  and 
extension  of  the  first  roots  formed  by  a  seedling  is 
a  necessity  for  almost  all  plants.  After  the  main 
root  has  bored  down  into  the  soil,  it  finds  the  food 


40  THE  NATURE  AND    WORK  OF  PLANTS 

substances  distributed  equally  in  all  directions  frc  m 
it.  To  secure  this  the  branches  drive  their  tips 
horizontally  or  nearly  so,  taking  a  course  nearly 
parallel  to  the  surface  of  the  soil.  The  positions 
attained  by  these  secondary  roots  may  be  seen  if  a 
young  bean  or  tomato  plant  is  carefully  dug  from 
the  ground,  noting  the  position  of  the  main  roots 
and  the  branches  as  they  are  exposed  to  view. 

45.  Sensitiveness  of  the  roots  to  moisture.  —  Both 
lateral  and  main  roots  may  encounter  other  forces, 
which  cause  them  to  bend  away  from  the  direc- 
tions taken  in  response  to  gravity  as  described  in 
the  previous  paragraphs.  The  action  of -unevenly 
distributed  moisture  may  be  shown  as  follows :  Place 
some  germinating  peas  in  a  deep  cigar  box  full  of 
garden  soil.  They  should  be  planted  in  the  ordi- 
nary manner  near  the  middle  of  the  box.  Give  the 
seedlings  barely  enough  water  to  keep  the  soil  moist 
at  one  end  of  the  box.  Pour  the  necessary  amount 
from  a  cup  on  the  soil  just  inside  one  end  and  allow 
it  to  diffuse  toward  the  plants.  The  quantity  should 
be  so  small  that  the  soil  in  the  other  end  of  the  box 
will  become  quite  dry.  After  a  growth  of  two  weeks 
turn  the  box  upside  down,  shake  out  the  plant,  and 


THE  ROOTS  41 

observe  the  position  of  the  roots.  Note  the  direction 
of  the  tips,  and  compare  the  number  and  length  of 
those  in  the  moist  end  of  the  box  with  those  in  the 
other  end.  This  sensitiveness  of  roots  to  moisture, 
by  which  they  are  attracted  toward  it,  causes  cisterns 
and  drains  to  become  filled  with  the  roots  of  clovers, 
grasses,  willows,  and  elms. 

46.  Boots  hend  aivay  from  light.  —  The  course 
taken  by  roots  in  response  to  gravity  and  moisture 
usually  leads  them  deeper  into  the  soil  and  away  from 
the  light,  but  they  have  the  power  of  bending  away 
toward  darkness  if  the  soil  should  be  taken  from 
above  them.  This  may  be  demonstrated  in  the 
following  manner :  Tie  a  piece  of  muslin  over  a 
tumbler  and  punch  a  number  of  holes  in  it  with  a 
bodkin.  Fill  the  tumbler  completely  full  with  water. 
Lay  some  germinating  seeds  of  the  radish  on  the 
muslin  with  the  roots  directed  through  the  holes  in 
the  cloth.  Set  in  a  window  where  it  may  receive  a 
strong  light.  Add  enough  water  daily  to  keep  the 
vessel  full.  Observe  the  positions  of  the  roots  from 
day  to  day.  The  tips  will  be  seen  to  be  directed 
away  from  the  point  from  which  the  light  comes, 
and  they  crowd  toward  the  inner  side  of  the  tumbler. 


42  THE  NATURE  AND    WORK  OF  PLANTS 

47.  The  tip  of  the  root  is  protected  hij  a  sheath- 
ing cap.  —  The  delicate  tip  of  the  root  is  pushed 
through  the  soil  very  rapidly,  and  its  apex  must  be 
protected  or  it  would  be  torn  by  the  rough  edges  of 
the  rock  particles.  This  may  be  readily  realized 
when  it  is  found  that  the  pressure  by  which  the 
root  is  driven  forward  is  equal  to  fifteen  or  twenty 
atmospheres,  or  two  or  three  hundred  pounds  to  the 
square  inch,  much  greater  than  that  exerted  by  steam 
in  a  locomotive  boiler. 

If  the  root  meets  a  soft  or  yielding  substance,  it 
bores  through  it  precisely  as  you  might  push  a 
large  needle  through  the  same  mass.  The  young 
roots  of  rapidly  growing  plants  are  often  seen  to 
penetrate  soft  or  decaying  wood,  or  even  the  large 
roots  of  other  plants.  The  actual  tip  of  the  root 
proper  is  composed  of  extremely  delicate  cells,  with 
the  thinnest  coverings  in  the  way  of  cell  walls,  and 
they  would  be  crushed  by  the  lightest  touch  of  any 
hard  object.  These  cells  are  of  importance  because 
by  theh  division  the  tissues  of  the  new  portions  of 
the  root  are  formed.  To  protect  the  delicate  mass 
of  living  matter  most  roots  are  furnished  with  a 
sheath  or  ca/9  on  the  tip.  This  root-cap  has  come 
to   serve    other   purposes    as    well,   and    it    may   be 


THE  BOOTS  43 

found  on  aquatics  covering  the  tips  of  roots  which 
hang  down  in  the  water  and  do  not  touch  any  hard 
object.  In  such  examples  the  sheath  is  generally 
very  long,  extending  back  over  the  younger  portion 
of  the  root,  and  as  it  is  filled  with  bitter  substa^nces 
it  prevents  swimming  animals  from  eating  or  injur- 
ing the  tips  of  the  roots.  It  may  be  seen  with 
difficulty  on  land  plants,  but  on  aquatics,  such  as 
the  water  hyacinth,  it  is  a  fourth  of  an  inch  long, 
and  may  be  pulled  off  and  examined  with  the  eye, 
or  better  by  the  aid  of  a  hand  lens.  A  sketch  of 
the  appearance  of  the  root  should  be  made,  and  a 
number  of  species  should  be  examined  in  search 
for  this  protecting  cap. 

48.  The  sensitiveness  of  roots  to  touch  or  contact 
with  solid  objects.  —  The  root-cap  would  not  be  suf- 
ficient to  protect  the  tip  of  the  root  from  all  danger 
of  injury  if  it  were  pushed  forward  in  a  straight 
line  and  did  not  turn  aside  for  an  obstruction.  As 
a  means  of  avoiding  injury  from  this  cause  the 
root  has  become  sensitive  to  the  touch  or  contact 
of  hard  objects,  in  such  manner  that  it  bends  away 
from  them.  This  may  be  seen  by  the  repetition 
01    one    of   Darwin's    classical    experiments.     Fix   a 


44  THE  NATURE  AND    WORK  OF  PLANTS 

seedling  to  a  cork,  as  in  §  43,  using  a  very  long 
pin,  but  placing  the  root  with  the  tip  pointing 
downward  but  not  touching  the  water  or  the  cork. 
Now  cut  the  smallest  bit  of  paper  you  can  handle, 
and  fasten  to  one  side  of  the  extreme  tip  by  means 
of  gum  arable  softened  in  water,  or  shellac.  Observe 
four  or  five  hours,  and  a  day  later,  and  the  apex 
of  the  root  will  be  seen  to  have  curved  away  from 
the  side  to  which  the  paper  was  attached,  exactly 
as  it  would  bend  away  from  a  hard  object  in  its 
path.  Some  difficulty  may  be  experienced  in  attach- 
ing the  paper  properly,  and  the  experiment  should 
be  repeated  until  some  decisive  result  is  at  hand. 

49.  The  roots  of  air  p7«n#s.  —  There  are  a  large 
number  of  species  which  inhabit  the  warmer  coun- 
tries that  never  reach  the  soil,  but  live  upon  the 
branches  of  trees,  to  which  they  cling  by  means  of 
climbing  roots,  such  as  were  mentioned  in  §  28. 
They  also  form  long  cordlike  roots  which  hang 
downward  sometimes  twenty  or  even  forty  feet  in 
length,  with  the  diameter  of  a  lead  pencil.  In 
some  instances  these  reach  the  soil,  and  then 
branches  are  formed.  Generally,  however,  these 
aerial  roots  are  papery  white  in   color   and  have  a 


THE  ROOTS  45 

curious  crinkled  appearance,  especially  in  the  case 
of  orchids.  This  is  due  to  the  peculiar  structure 
of  the  outer  layers  of  cells.  In  fact,  these  roots 
have  a  layer  of  tissue  not  found  in  ordinary  roots. 
This  outer  tissue  is  composed  of  cells,  which  die  as 
soon  as  they  attain  full  size,  and  the  walls  are 
left,  forming  a  layer  of  loose  spongy  tissue  entirely 
sheathing  the  root.  The  sj^ongy  layer  not  only 
absorbs  drops  of  water  which  may  fall  upon  it, 
but  will  also  gather  water  from  the  air  when  it  is 
humid  and  damp.  The  species  furnished  with  such 
roots  usually  live  in  localities  which  have  much 
rain,  and  their  entire  supply  of  water  may  be 
gathered  in  these  ways. 

50.  Parasitic  roots.  —  Many  species  have  the 
habit  of  fastening  to  the  bodies  of  other  plants 
and  drawing  a  part  or  all  of  their  water  and  food 
from  them.  They  do  not  need  the  ordinary  soil 
roots,  but  have  developed  special  forms  which  are 
capable  of  piercing  the  bodies  of  their  hosts,  as  the 
plants  on  which  they  live  are  called.  The  mistletoe 
is  an  example  of  this  type ;  but  perhaps  the  para- 
site most  widely  distributed  in  America  is  the 
dodder  {Cuscuta),    which    may    be    seen    in    damp 


46  THE  NATURE  AND    WORK  OF  PLANTS 

meadows  in  July  and  August,  twining  around  the 
stems  of  almost  any  herbaceous  plant,  forming 
numerous  coils  of  yellow  or  cream-colored  flowers. 
If  the  host  plant  is  taken  up  and  the  nature  of 
the  union  between  the  two  is  examined,  it  will  be 
seen  that  the  parasitic  dodder  sends  a  large  number 
of  small  blunt  projections  or  knobs  of  tissue  into 
the  stem  of  the  host.  These  are  the  roots,  and 
they  may  arise  at  any  point  on  the  stem  of  the 
dodder,  and  their  function  is  the  absorption  of  the 
sap  of  the  host  plant. 

51.  Method  of  germination  and  groiuth  of  the 
dodder.  —  The  seed  of  the  dodder  germinates  on  the 
ground,  sending  up  a  long  threadlike  stem  which 
waves  about  slowly  in  the  air  until  its  tip  comes  in 
contact  with  the  stem  of  another  species,  when  it 
coils  around  it  and  sends  out  its  roots.  The  roots 
are  seen  to  arise  only  at  points  where  the  parasite 
touches  the  stem  of  the  host.  If  the  seed  of  the 
dodder  is  planted  in  a  pot  with  a  young  tomato 
plant  or  castor  oil  plant,  this  may  be  observed.  It 
may  be  seen  also  that  the  only  root  formed  at  the 
base  of  the  stem  on  the  germination  of  the  seed  is  a 
short  peg-shaped  structure,  and  that  it  simply  holds 


THE  BOOTS  47 

tlie  seedling  in  place  until  it  has  found  a  host  to 
which  it  can  fasten.  As  soon  as  this  is  accom- 
plished, the  soil  root  and  the  lower  part  of  the 
stem  of  the  dodder  dies  away,  leaving  it  entirely 
supported  on  the  body  of  its  host. 

52.  Union  of  7'oots  ivitJi  fungi.  —  Quite  a  large 
number  of  the  higher  plants  form  what  are  known 
as  mycorrhizas.  A  mycorrhiza  is  the  structure  which 
results  from  the  union  of  roots  or  absorbing  organs 
with  the  tubelike  hyplice  or  threads  of  a  mushroom 
or  mould  in  the  soil.  This  union  is  of  benefit  to 
both  the  fungus  and  the  higher  plant.  In  some 
instances  the  fungus  lives  inside  the  root,  and  in 
others  it  forms  a  layer  of  threads  on  the  outside. 

If  the  smaller  roots  of  the  beech,  oak,  or  any  of 
the  pines  are  dug  up,  a  number  of  short  club-shaped 
branches  may  be  seen  which  are  brownish  in  color. 
These  short  branches  are  inhabited  by  fungi  and  are 
mycorrhizas.  A  second  example  may  be  sought  for 
in  the  waxy  white  "  Indian  pipe  "  or  "  corpse  plant  " 
[Monotropa)  which  grows  in  deep  woods.  Its  short 
bunches  of  curiously  shaped  roots  are  covered  with 
a  layer  of  felt  made  up  of  the  threads  of  the 
fungus.     The  higher  plant  gets  practically  all  of  its 


48  THE  NATURE  AND   WORK  OF  PLANTS 

food  from  the  fungus,  and  it  therefore  has  no  need  of 
true  green  leaves.  It  has  lost  these  organs  in  times 
past  because  of  the  very  fact  that  it  ceased  to  use 
them.  It  is  true  of  all  living  things,  that  as  soon  as 
an  organ  ceases  to  be  used  or  to  be  useful,  it  is  devel- 
oped less  perfectly  on  each  succeeding  generation  of 
individuals  until  perhaps  only  a  rudiment  remains. 
This  is  illustrated  by  the  coral-root  {Corallorhiza),  a 
reddish  orchid  common  throughout  the  Northern 
states.  This  plant  has  not  only  reduced  its  leaves, 
but  on  account  of  the  activity  of  the  fungus  in 
supplying  it  with  food,  the  roots  have  been  entirely 
lost,  the  fungus  of  the  mycorrhizas  now  living  in 
the  short  underground  stems  which  have  the  appear- 
ance of  a  bunch  of  coral. 

53.  Roots  as  storage  organs.  —  During  the  sum- 
mer season  the  plant  manufactures  much  more  food 
than  it  can  use  at  that  time,  and  the  surplus  is 
stored  up  until  needed.  The  amount  thus  accumu- 
lated is  often  sufficient  to  feed  the  plant  through  sev- 
eral successive  seasons  in  case  it  had  no  opportunity 
to  make  its  usual  supply.  Various  parts  of  the  body 
are  selected  as  places  of  storage.  The  beet  is  an 
example  of  a  root  and  a  small  portion  of  a  stem  be- 


THE  ROOTS  49 

ing  used  for  the  storage  of  sugar.  The  sweet  potato 
family  deposit  the  reserve  food  in  the  form  of  starch 
in  the  roots,  which  become  extremely  large,  as  may 
be  seen  in  the  cultivated  form.  One  of  this  family, 
the  "  man  of  the  earth  "  {Ipomea  pandurata),  enlarges 
the  main  root  and  deposits  starch  and  oil  in  it  until 
it  reaches  a  length  of  several  feet,  a  diameter  of  six 
to  eight  inches,  and  weighs  as  much  as  twenty 
pounds.  It  is  to  be  borne  in  mind  that  not  all  parts 
of  the  plant  found  imderground  are  roots.  Many 
species  have  stems  which  live  very  much  like  roots 
and  resemble  them  in  general  appearance.  They 
may  be  separated  from  them,  however,  by  the 
absence  of  the  root-cap,  and  by  the  fact  that  they 
show  joints,  or  nodes,  and  produce  huds,  although 
the  roots  of  the  sweet  potato  are  also  capable  of 
giving  rise  to  buds. 

54.  Metliod  of  growth  of  roots.  —  Another  fea- 
ture which  distinguishes  roots  from  stems  is  the 
method  of  growth.  Germinate  a  pea  or  bean,  as 
shown  in  §  34,  until  the  main  root  is  two  or  three 
inches  long,  then  mark  it  off  in  sections  a  quarter  of 
an  inch  long  by  means  of  lines  of  India-ink  applied 
by  means  of   a   thread  or  a  thin  splinter  of  wood. 


50  THE  NATURE  AND    WORK  OF  PLANTS 

Measure  the  distance  between  the  marks  daily  for  a 
week.  In  what  part  of  the  root  does  most  of  the 
growth  take  place  ?  Compare  with  the  growth  of 
roots  (§  54),  leaves  (§  113),  and  stems  (§§  144-151). 

55.  Absorhing  and  fixing  organs  of  the  lower 
2)lants.  —  Roots  represent  the  most  highly  perfected 
organs  for  the  fixation  of  the  plant  in  its  position 
and  the  absorption  of  food.  In  the  lower  forms, 
incapable  of  building  such  complex  organs,  these 
functions  must  be  carried  on  by  simpler  structures, 
which  perhaps  must  take  other  and  additional 
work. 

56.  Ahsorhing  and  fixing  organs  of  the  ferns, 
7nosses,  and  Uvenvorts.  —  Among  the  ferns,  mosses, 
and  liverworts  absorption  and  fixation  are  carried 
on  chiefly  by  means  of  large  tubes  termed  rhizoids, 
which  resemble  root-hairs  except  in  size  and  heavi- 
ness of  the  walls,  although  rootlike  organs  are  pres- 
ent in  some  species.  Some  of  these  forms  are  very 
much  like  the  higher  plants,  in  which  instance  the 
large  rhizoids  are  attached  to  the  underground  parts 
like  root-hairs.  In  other  instances  the  plant  is  in 
the  form  of  a  leaflike  body,  which  lies  on  the  surface 
of  the  ground.     The   rhizoids  spring   directly  from 


THE  ROOTS  61 

the  lower  side  of  the  flattened  body  and  penetrate 
the  soil,  accomplishing  both  fixation  and  absorption. 
Each  little  tube  is  very  delicate,  yet  their  combined 
strength  is  sufficient  to  hold  the  body  quite  firmly  in 
position.  The  thin  bodies  of  the  ordinary  liverwort 
(Marchantia  jjolijmorpha  or  Conocephalus)  should  be 
examined  and  the  character  of  the  rhizoids  noted. 
They  will  be  seen  as  a  tangled  mass,  to  which  are 
adhering  great  numbers  of  particles  of  soil. 

57.  Method  of  fixation  of  the  moulds  and  7mtsh- 
rooms.  —  Find  a  number  of  freshly  grown  mush- 
rooms or  "  toadstools  "  in  the  ground  in  the  woods, 
and  carefully  dig  away  the  soil  from  around  the  base 
of  the  stalk  supporting  the  umbrella-like  top.  Run- 
ning away  from  the  base  of  this  stalk  are  a  number 
of  ragged-looking  grayish  strands,  and  if  these  are 
followed  out  farther,  they  will  be  seen  to  divide  and 
subdivide  into  still  smaller  strands.  These  strands 
constitute  the  absorbing  and  fixing  part  of  the  plant, 
and  they  are  made  up  of  a  great  number  of  tulles. 
Bundles  of  tubes  branch  off  separately  and  in  small 
groups  all  along  the  main  strands,  giving  them  the 
peculiar  ragged  appearance.  These  organs  penetrate 
the  soil  to  great  distances,  living  and  growing  during 


52  THE  NATURE  AND   WORE  OF  PLANTS 

all  of  the  Wcarm  season,  absorbing  the  substances 
set  free  by  the  decay  of  other  plants.  At  certam 
times  they  send  up  the  large  branches  which  are 
ordinarily  know  as  mushrooms,  which  bear  innumer- 
able spores,  and  which  reproduce  the  plant.  The 
mycelium,  or  mass  of  tubes,  spreads  rapidl}^  under- 
ground, and  the  mushrooms  may  appear  in  the  most 
unexpected  places  and  very  suddenly.  Like  the 
roots  of  the  higher  plants,  they  are  driven  upward 
through  the  soil  with  great  force,  and  may  be  seen 
to  lift  stones,  large  pieces  of  wood,  or  heavy  clods  of 
earth.  Mushrooms  have  been  known  to  grow  up 
under  the  stones  of  the  sidewalks  in  village  streets, 
lifting  them  from  their  places  and  seriously  dis- 
arranging the  pavement. 

58.  Ahsorptio7i  and  fixation  hy  the  algce,  and  bac- 
teria. —  Many  of  the  plants  of  the  lowest  groups 
are  completely  submerged  in  water  in  which  their 
food  is  dissolved,  and  as  a  consequence  they  absorb 
food  over  their  entire  surfaces.  Some  of  these,  espe- 
cially the  bacteria,  are  in  the  form  of  small  globular 
or  egg-shaped  cells,  or  in  the  form  of  rods  joined 
together  in  a  chain,  all  floating  freely  in  the  water. 
The    function  of   fixation  is  clearly  absent  in  most 


THE  ROOTS  53 

instances,  and  absorption  is  carried  on  by  the  entire 
body.  Some  of  these  organisms  accomplish  fixation 
in  certain  stages  of  their  existence  by  means  of  jelly- 
like substances  outside  their  walls.  Some  of  these 
floating  forms  run  out  minute  threads  of  protoplasm, 
with  which  they  lash  the  water  in  such  manner  as 
to  swim  from  place  to  place.  Others,  with  single 
or  many  celled  bodies,  make  holdfasts,  or  fixing 
roots,  with  which  they  attach  themselves  to  the 
rocks  or  the  bottom  of  the  pond  or  stream. 

A  general  idea  of  the  nature  of  these  organisms 
may  be  gained  by  an  examination  of  the  pond-scums 
(Spirogyra),  which  float  near  the  surface,  and  are 
made  up  of  a  number  of  long  threads,  each  thread 
being  formed  by  the  division  and  growth  of  num- 
bers of  rod-shaped  green  cells. 


V.   THE   LEAVES 

59.  Structure  of  leaves.  —  Examine  the  leaves  of 
the  oak,  maple,  beech,  and  willow  on  the  stems. 
The  leaf  will  be  found  to  consist  of  three  principal 
parts :  the  hase  or  portion  by  which  it  is  attached  to 
the  stem,  the  stalk  or  j^etiole,  and  the  blade  or  lamina. 
The  base  may  take  the  form  of  a  swelling  of  the 
petiole,  as  in  the  locust,  bean,  or  sumach,  or  it  may 
develop  small,  leaflike  appendages,  as  in  the  w^illow. 
Make  an  examination  of  the  leaf  of  the  willow  and 
draw  to  show  results  of  observations. 

The  petiole  is  generally  in  the  form  of  a  stalk  or 
stem,  though  it  may  be  edged  or  winged,  or  it  may 
be  absent,  in  which  case  the  lamina  of  the  leaf  sits 
directly  on  the  stem.  Find  some  jDlant  the  leaves  of 
w^hich  are  lacking  in  petioles,  and  draw. 

The  base  and  the  petiole  are  for  the  purpose  of 
supporting  the  lamina  in  the  proper  position,  and 
conducting  water  and  food  to  it.  It  is  in  the  lamina 
that  the  most  important  work  of  the  leaf  is  done. 

64 


THE  LEAVES  55 

Now  make  a  careful  examination  of  the  blades  of 
the  leaves  you  have  brought  together.  Trace  the 
exact  outlines  on  a  piece  of  paper.  Are  the  margins, 
cut  to  the  same  pattern  ?  Compare  the  upper  and 
lower  sides  of  the  leaves.  The  upper  side  is  fairly 
smooth  and  even,  while  the  lower  is  rougher  and 
shows  numbers  of  ridges  or  nerves,  which  may  be 
seen  only  faintly  on  the  upper  side.  Fill  out  the 
outline  of  each  leaf  with  a  tracing  of  the  nerves.  It 
will  be  found  that  the  nerves  start  from  the  base  of 
the  leaf  or  from  a  median  midrib  and  divide  and 
subdivide,  running  to  all  parts  of  the  blade.  The 
space  between  the  nerves  is  filled  by  a  soft  green 
tissue,  the  mesojjliyl,  and  the  nerves  serve  as  a 
framework  to  hold  it  in  position.  By  searching 
among  the  beds  of  dead  leaves  in  the  woods  old 
specimens  may  be  found  from  which  the  mesophyl 
has  decayed,  leaving  the  network  of  the  nerves 
almost  entire.  The  lower  surface  of  the  leaf  is  fur- 
nished with  thousands  of  minute  openings,  the 
stomata.  These  are  usually  so  small  that  they  may 
not  be  seen  even  with  a  hand  lens ;  but  if  some  of  the 
flattish  fronds  of  the  liverwort  (Conocejjhalus)  can 
be  found,  they  may  be  seen  on  the  upper  surface 
with  the  naked  eye. 


66  THE  NATURE  AND    WORK  OF  PLANTS 

The  entire  leaf,  as  well  as  that  of  the  body  of 
the  seed-plant,  is  covered  with  a  thin  sheet  of  cells, 
the  epidermis.  The  epidermis  may  be  peeled  off  in 
whitish  strips  by  using  a  needle,  or  point  of  a  sharp 
knife. 

60.  Leaves  with  both  surfaces  alike.  —  The  leaves 
examined  in  the  preceding  paragraph  are  held  in  a 
horizontal  position  on  the  stems.  Examine  leaves 
that  are  held  in  an  upright  position  or  nearly  so,  like 
those  of  the  narcissus,  iris,  or  lily.  The  nerves  will 
not  be  so  apparent,  and  both  surfaces  present  nearly 
the  same  appearance  and  would  show  about  the 
same  arrangement  of  the  cells. 

61.  Compound  leaves. — Examine  the  leaves  of 
the  locust,  pea,  bean,  or  sumach.  The  three  principal 
parts  may  be  found,  but  the  lamina  appears  to  be 
branched  or  cut  up  into  a  number  of  smaller  leafiets, 
each  with  its  own  stalk  by  which  it  is  fastened  to 
the  midrib  or  r^hachis  of  the  leaf.  The  number  of 
leaflets  in  the  bean  is  three  (see  also  §  217).  Deter- 
mine the  number  in  the  locust,  pea,  and  other  speci- 
mens you  may  find.  The  compound  leaf  is  capable 
of  doing  more  work  than  the  simple  forms  showing 
the  same  extent  of  lamina. 


THE  LEAVES  57 

62.  Comjjosition  of  the  air.  —  The  leaves  are 
generally  held  aloft  in  the  air,  and  since  they  come 
into  contact  with  no  other  medium,  it  is  plain  that 
the  composition  of  the  air  will  be  of  great  interest 
to  any  one  studying  the  activity  of  leaves.  The  air 
is  made  up  of  nitrogen,  carbonic  acid  gas,  oxygen, 
argon,  and  perhaps  other  rare  gases  in  small  quanti- 
ties. Besides,  watery  vapor,  and  traces  of  acids  are 
present  in  a  proportion  which  varies  greatly  with  the 
locality.  In  10,000  gallons  of  ordinary  air  would  be 
found  about  7795  gallons  of  nitrogen,  2061  gallons 
of  oxygen,  4  gallons  of  carbon  dioxide,  140  gallons 
of  water,  and  small  amounts  of  the  other  constitu- 
ents. These  gases  and  vapors  are  not  united  to  form 
a  compound.  Thus  hydrogen  and  oxygen  are  united 
to  form  the  compound  water,  but  the  gases  of  the  air 
are  simply  mixed  together  without  actually  uniting. 

63.  Gases  of  use  to  the  plant.  —  The  oxygen  and 
carbon  dioxide  are  of  the  greatest  importance  to  the 
plant.  Nitrogen  of  the  air  is  of  no  use,  except  to 
mix  with  and  dilute  the  other  gases.  Only  a  few 
species  are  capable  of  taking  this  gas  and  using  it 
as  food.  This  element  is  usually  gained  from  com- 
pounds in  the  soil. 


58  THE  NATURE  AND    WOBK  OF  PLANTS 

The  water  of  the  air  is  rarely  used  by  the  plant, 
yet  its  presence  prevents  the  plant  from  drying  out, 
and  it  is  of  great  importance  in  this  way.  The  other 
substances  are  more  or  less  useful  or  harmful,  accord- 
ing to  the  quantities  present. 

64.  Functions  of  the  leaf.  —  To  the  leaf  is  in- 
trusted the  work  of  taking  in  the  carbon  dioxide 
of  the  air,  splitting  it  up,  and  combining  it  with 
water  sent  up  from  the  roots,  in  such  manner  as 
to  form  sugars.  The  stream  of  water  also  brings 
up  mineral  substances  from  the  roots  which  are 
needed  in  the  leaf.  The  amount  of  water  which 
thus  reaches  the  leaf  is  much  greater  than  can  be 
used  in  the  tissues,  and  most  of  it  must  be  thrown 
off.      This  is  also  done  by  the  leaf, 

65.  The  colors  of  leaves.  —  The  leaves  of  most 
species  are  colored  green  by  the  presence  of  a  sub- 
stance the  botanist  terms  chlorophyl,  and  this  pig- 
ment is  also  found  in  the  outer  tissues  of  some  stems, 
branches,  or  even  roots.  It  is  formed  in  special 
masses  of  protoplasm,  and  the  depth  of  the  green 
color  of  the  leaf  depends  on  the  number  of  these 
masses  in  the  cells.     Then   again  the  living  matter 


THE  LEAVES  69 

has  the  power  of  moving  the  masses  of  pigment 
toward  and  away  from  the  surface  so  that  the  tone 
of  color  may  change  in  the  same  leaf  during  the 
course  of  a  few  hours. 

Besides  the  green,  other  coloring  matter  may  be 
present  in  the  cells,  or  the  walls  may  be  dyed.  The 
leaf  may  show  a  certain  color  because  of  the  contents 
of  its  cells,  or  because  of  the  color  of  its  walls,  in 
the  same  manner  that  a  bottle  of  liquid  may  appear 
blue  because  of  the  color  of  the  liquid,  or  the  tint 
of  the  glass. 

66.  Hidden  chlorophjl.  —  Chlorophyl  may  be 
hidden  because  of  the  presence  of  other  colors. 
The  leaves  of  the  amaranth,  cockscomb,  and  many 
other  species  appear  to  be  dark  red  in  color,  and  no 
chlorophyl  is  to  be  seen.  That  it  is  j^i'esent,  how- 
ever, may  be  shown  by  the  following  experiment: 
Place  a  colored  leaf  as  above,  in  a  dish  of  cold  water, 
and  bring  it  to  a  boil  over  a  stove  or  spirit  lamp.  If 
this  is  continued  for  a  few  minutes,  the  red  color 
will  be  extracted,  and  the  normal  green  of  the  leaf 
will  be  visible.  The  experiment  also  shows  that  red 
coloring  matter  is  soluble  in  water,  while  chlorophyl 
is  not. 


60  THE  NATURE  AND    WORK  OF  PLANTS 

67.  Characteristics  of  chloi^ojyhyl.  —  Chloropb.yl  is 
absolutely  indispensable  for  the  formation  of  food  in 
the  leaf,  and  it  will  be  important  to  extract  some  of 
it  from  a  leaf  and  ascertain  its  qualities.  To  do  this 
place  a.  number  of  leaves,  that  have  been  cut  up  into 
small  pieces  or  bruised,  in  a  bottle  or  tumbler  and 
cover  with  alcohol.  Close  the  vessel  and  set  away 
in  a  dark  place  for  a  day.  Pour  off  some  of  the 
liquid  into  a  wine-glass  or  small  test  tube.  Hold  up 
to  the  light.  The  solution  appears  to  be  of  a  bright 
emerald  green.  Now  hold  the  glass  in  direct  sun- 
light and  look  at  the  edge  of  the  liquid.  If  held 
properly,  it  will  show  a  blazing  red  appearance. 
Chlorophyl  has  the  power  of  making  such  changes 
in  sunlight  that  it  appears  red;  it  affects  light  in 
other  ways  also. 

68.  S2:)ectrum  of  chlorophyl. — If  the  study  of 
chlorophyl  were  continued  in  the  physical  labora- 
tory, it  could  be  seen  that  if  light  which  has  passed 
through  a  solution  of  chlorophyl  is  spread  out  on  a 
screen  by  means  of  a  prism  of  glass,  some  of  the 
colors  of  the  artificial  rainbow  will  be  missing.  The 
missing  parts  will  comprise  the  blue,  violet,  and  most 
of  the  red  rays.     Chlorophyl,  in  the  living  plant,  ab- 


THE  LEAVES  61 

sorbs  these  rays,  and  the  energy  derived  from  them 
enables  protoplasm  to  carry  on  the  work  of  food- 
making. 

69.  The  leaf  is  a  machine  or  a  mill.  —  If  the  ac- 
tivity of  chlorophyl  might  be  described  in  another 
way,  it  could  be  said  that  the  leaf  is  an  engine.  The 
chlorophyl  would  be  the  boiler,  and  when  light  falls 
upon  it  energy  or  power  is  set  free,  which  causes 
the  engine  to  move  or  perform  work,  as  when  heat 
is  applied  to  the  boiler  of  a  steam  engine.  The  leaf 
is  a  solar  engine  and  gets  its  energy  from  light 
instead  of  heat  rays.  The  power  acquired  from  light 
by  chlorophyl  drives  the  protoplasmic  machinery  and 
enables  it  to  take  water  and  carbon  dioxide  and 
make  sugar  from  them,  throwing  off  certain  things 
not  used  in  the  process.  After  the  formation  of 
sugar  it  is  combined  with  nitrogen  and  other  ele- 
ments before  it  can  become  a  part  of  the  living 
matter. 

70.  Quality  of  light  most  useful  to  the  plant. — 
Prepare  two  boxes  of  seedlings.  The  boxes  should 
be  at  least  six  or  eight  inches  deep,  and  the  plants 
should  be  grown  in  a  thin  layer  of  soil  at  the  bot- 
tom of  the  box.     Cover  one  box  with  a  sheet  of  win- 


62  THE  NATURE  AND    WORK  OF  PLANTS 

dow  glass  and  red  tissue  paper,  and  the  other  with 
glass  and  blue  paper,  and  set  in  a  sunny  place.  Care 
for  the  plants  from  day  to  day,  and  compare  their 
growth  at  the  end  of  a  week.  This  will  determine 
whether  the  blue  or  red  rays  -are  most  useful  to 
the  plant,  and  will  also  recall  the  mistaken  "blue 
glass  "  craze  of  a  few  years  ago. 

71.  LigJit  destroys  chlorophyl.  —  Place  a  portion 
of  the  solution  of  chlorophyl  prepared  in  §  67  in 
the  sunlight,  and  the  remainder  in  a  dark  closet. 
Compare  the  color  of  the  two  in  a  few  days.  The 
one  in  the  light  will  be  seen  to  have  faded.  The 
fading  action  of  light  goes  on  in  the  leaf  con- 
stantly, but  the  green  color  is  constantly  restored 
by  the  protoplasm.  If  a  plant  should  be  exposed 
to  a  light  much  stronger  than  that  to  which  it  is 
accustomed,  the  fading  will  take  place  faster  than 
the  living  matter  could  mend  it,  and  the  leaf  would 
turn  yellow  and  die. 

72.  Light  is  necessary  for  the  formation  of  chlo- 
rophyl in  most  instances.  —  While  light  slowly  breaks 
down  chlorophyl,  yet  the  plant  usually  cannot  form 
its  substance  without  the  aid  of  light.  Place  a 
bulb   of   canna,  jack-in- the-pulpit,  or  a  seed   of   the 


THE  LEAVES  63 

pea  or  bean  in  proper  soil  in  a  pot  and  set  in  a 
dark  cellar  and  then  cover  with  a  bucket  or  a  box. 
Give  the  seedling  the  proper  amount  of  water,  which 
will  be  less  than  if  grown  in  light.  After  a  time 
shoots  will  be  formed  which  will  be  very  much 
different  from  those  grown  from  similar  seedlings 
or  plants  in  the  light. 

Lay  a  broad  board  on  the  grass,  and  note  the 
color  of  the  blades  beneath  a  week  later.  Not  only 
will  the  chlorophyl  be  absent,  but  the  stems  and 
leaves  will  be  greatly  changed  in  form  and  size. 
The  stems  will  be  two  or  three  times  as  long  as 
usual.  This  seems  to  be  a  method  by  which  the 
plant  gets  its  leaves  and  stems  up  to  sunlight  when 
they  are  covered  by  anything  or  overshadowed  by 
other  plants.  Species  like  the  narcissus,  which  have 
sword-shaped  leaves  with  no  petiole  or  stem  above 
ground,  elongate  the  blade  of  the  leaf  itself  in  this 
effort  to  get  up  to  light. 

73.  Cajmcity  of  leaves  for  the  ahsorption  of  light. 
—  Take  any  tube  of  wood,  metal,  or  paper  an  inch 
or  more  in  diameter,  and  fasten  a  leaf  over  the  end. 
This  may  be  done  by  turning  the  margins  back  over 
the  tube  and  tying  a  string  around  the  tube  at  that 


64  THE  NATURE  AND    WORK  OF  PLANTS 

point.  Hold  the  tube  with  this  end  pointing  di- 
rectly toward  the  sun,  and  put  the  eye  at  the  other 
end.  Can  any  light  be  seen  through  the  leaf?  If 
so,  add  another  leaf  and  test  again.  How  many 
leaves  are  necessary  to  take  up  all  the  light?  If 
several  kinds  of  leaves  are  tested  in  this  way,  it 
will  be  found  that  those  of  different  species  vary 
greatly  in  their  light-absorbing  power.  Do  you 
notice  any  connection  between  tliis  capacity  and 
the  place  in  which  the  species  grows  naturally? 

74.  Formation  of  food  in  chlorophyl-hearing  organs. 
—  The  carbon  dioxide  of  the  air  is  used  by  the 
plant  in  making  food.  This  compound  consists  of 
two  volumes  of  oxygen  and  one  of  carbon.  It  is 
taken  into  the  leaf  through  openings  on  the  lower 
surface  and  passes  through  the  thin  walls  of  the 
cells  containing  chlorophyl.  It  is  then  split  in  two 
parts,  and  the  carbon  is  combined  with  the  oxygen 
and  hydrogen  of  water  to  form  a  sugar.  Most  of 
the  oxygen  is  thrown  off.  All  of  these  steps  may 
not  be  followed,  even  in  the  best-equipped  laboratory, 
but  if  the  leaf  of  any  water  plant  growing  in  the 
sunlight  is  observed,  it  may  be  seen  to  give  off  small 
bubbles  of  oxygen.     This  may  be  best  seen  by  plac- 


THE  LEAVES  65 

ing  a  small  aquatic  plant  in  a  tumbler,  or  the  leaf  of 
a  land  plant  may  be  immersed  in  water  and  the 
formation  of  the  bubbles  noted. 

75.  Non-green  colors.  —  If  the  experiment  in  §  72 
is  repeated,  it  may  be  seen  that  red  and  other  colors 
are  formed  in  leaves  grown  in  darkness  as  well  as 
in  light.  This  may  be  illustrated  still  further  if  a 
flowering  branch  of  some  plant  is  thrust  through  a 
hole  in  the  wall  of  a  tight  pasteboard  box,  and  the 
flowers  allowed  to  open  in  darkness.  The  most 
noticeable  of  the  colors  that  are  found  in  leaves, 
beside  green,  is  red,  though  purples  are  also  abundant. 
All  shades  of  red,  blue,  and  yellow  are  to  be  seen  in 
flowers  and  fruits.  If  a  clump  of  rhubarb  is  made  to 
grow  in  a  dark  cellar,  the  leaves  and  stems  will  be 
blood  red. 

76.  Origin  of  red  colors.  —  Red  coloring  matter 
is  formed  most  freely  in  parts  of  the  plant  contain- 
ing much  sugar.  The  origin  of  coloring  matters  is 
not  well  understood.  It  has  been  determined,  how- 
ever, that  when  a  specimen  is  fed  with  sugar,  it  will 
manufacture  this  color  more  abundantly.  To  demon- 
strate this  action  a  species  should  be  selected  that 
has  the   power  of  making  the  color,  such   as   ivy, 


66  THE  NATURE  AND    WORK  OF  PLANTS 

Virginia  creeper,  columbine ;  and  a  cutting  composed 
of  a  large  branch  or  twig  should  have  the  lower  end 
immersed  in  a  stone  or  glass  jar  as  in  the  water  cul- 
tures previously  described,  §  13.  The  jars  should  be 
filled  with  water  from  a  stream  or  well  to  which  an 
ounce  of  sugar  or  glucose  has  been  added  for  each 
quart.  Compare  the  colors  of  the  leaves  with  others 
grown  in  the  same  kind  of  water  without  sugar,  and 
also  with  those  remaining  on  the  plant. 

This  experiment  may  be  repeated  if  living  speci- 
mens of  the  bladderwort  (Utricularia)  can  be  pro- 
cured. Place  some  specimens  in  a  shallow  dish  of 
water  and  set  in  the  sun.  Prepare  a  second  dish,  but 
add  the  proportion  of  sugar  used  in  the  last  test. 
Change  the  liquids  at  least  once  a  week.  Note  the 
depth  of  red  color  of  the  two  specimens.  Cold  and 
wounds  also  induce  the  formation  of  red  coloring 
matter. 

77.  Changes  in  color.  —  The  red  and  blue  colors 
appear  to  be  very  closely  connected,  because  the 
parts  of  a  plant  may  often  change  from  one  to  the 
other  in  the  course  of  a  few  days.  This  may  be 
noticed  in  the  flowers  of  the  peony,  as  well  as  in  the 
opening  buds  of   many  plants.      Note  the  color  of 


THE  LEAVES  67 

the  leaves  of  the  oak  and  maple  immediately  after 
the  buds  open  in  the  spring,  and  compare  with  that 
of  the  mature  organs.  Compare  also  the  colors  of 
ripe  and  unripe  fruits,  such  as  apples,  tomatoes, 
berries,  plums,  and  peaches. 

78.  Autumnal  colors.  —  The  colors  of  autumnal 
leaves  are  very  striking,  not  only  because  of  their 
depth  and  brilliancy,  but  because  they  appear  on 
so  many  leaves  and  so  many  plants  at  the  same 
time.  Furthermore,  the  plants  which  show  colors 
most  notably  are  trees  which  are  large  and  prominent 
features  of  the  landscape.  These  colors  embrace  a 
large  number  of  shades  and  tints  of  yellow,  red,  and 
purple,  and  they  are  probably  formed  from  the  sugar 
in  the  cells,  and  by  the  breaking  down  of  the  green 
color  into  yellows  and  browns.  Yellow  colors  are 
also  formed  independently,  or  appear  most  strikingly 
in  dying  leaves.  The  actual  changes  of  color  in  at 
least  one  species  should  be  followed  through  the 
months  of  September  and  October,  as  well  as  the 
colors  of  the  same  species  when  the  buds  open  in 
the  following  spring.  Although  the  autumnal  colors 
of  every  species  show  some  diversity,  yet  the  keynote 
is  fairly  constant.     The  birches  are  a  golden  yellow, 


68  THE  NATURE  AND    WORK  OF  PLANTS 

the  oaks  vary  through  yellow  orange  to  reddish 
brown,  the  red  maple  is  generally  a  scarlet  varying 
to  a  dark  red,  the  tulip  tree  a  light  yellow,  and 
sumachs  become  a  flaming  scarlet.  These  colors 
show  some  variation  with  the  amount  of  moisture 
and  character  of  the  soil. 

79.  Uses  of  autumnal  colors.  —  The  actual  pur- 
pose of  the  autumnal  colors  cannot  be  determined. 
There  is  no  doubt,  however,  that  their  presence  pre- 
vents damage  by  sunlight  to  delicate  substances 
which  are  withdrawn  from  the  leaf  to  the  stem 
before  they  are  cast  off. 

80.  Uses  of  red  and  other  colors  in  flowers  and 
fruits. —  The  purpose  of  the  brilliant  colors  of 
flowers,  fruits,  and  leaves  is  not  clearly  made  out. 
The  colors  of  flowers  may  serve  to  attract  insects, 
but  this  is  the  case  in  only  a  few  instances  An 
insect  is  attracted  to  a  flower  generally  by  the  scent 
of  nectar  or  honey,  and  it  recognizes  the  flower  by 
its  size  and  form  rather  than  by  the  color.  The 
same  is  true  of  fruits  which  need  the  aid  of  insects 
for  their  dissemination.  It  is  to  be  noted  that  very 
vivid  colors  are  often  found  in  the  centre  of  large 


THE  LEAVES  69 

objects,  such  as  the  sugar  beet,  or  large  fruits,  where 
they  could  not  possibly  be  of  any  use  whatever. 

81.  Characteristics  of  red  and  Hue  colors. — It 
has  been  shown  in  §  66  that  the  red  color  of  a  leaf 
of  coleus  may  be  extracted  by  water,  and  it  is  a 
matter  of  common  experience  that  the  colors  of  fruits 
are  easily  obtained  in  this  way.  If  red  coloring 
matter  is  examined  in  the  same  manner  as  chloro- 
phyl,  it  will  be  found  that  it  absorbs  different  rays 
of  light  than  those  taken  up  by  the  green  pigment. 

82.  Red  color  as  a  shield.  —  A  great  many  species 
are  furnished  with  a  layer  of  red  color  on  the  upper 
side  of  the  leaf.  This  absorbs  some  of  the  light 
which  strikes  the  leaf,  and  a  diminished  amount  is 
allowed  to  fall  upon  the  delicate  green  coloring 
matter  below.  The  action  of  the  red  then  would 
be  like  the  slats  of  a  shutter,  which  permit  only  a 
part  of  the  rays  to  shine  through.  The  presence 
of  the  red  would  be  beneficial  to  leaves  exposed  to  a 
degree  of  sunlight  stronger  than  they  are  otherwise 
adapted  to  bear. 

83.  Red  color  as  a  heat  producer.  —  The  rays  of 
light  that  are  taken  up  by  the  red  and  blue  colors 


iO  THE  NATURE  AND    WORK  OF  PLANTS 

are  converted  into  heat.  This  may  be  demonstrated 
if  two  naked-bulb  thermometers  are  procured.  Next 
find  a  species  wliich  has  some  of  its  leaves  green  and 
others  red,  such  as  canna  or  coleus.  Wrap  a  green 
leaf  around  the  bulb  of  one  and  secure  it  with  a 
small  string.  Place  a  red  leaf  around  the  bulb  of 
the  second  instrument.  Expose  them  side  by  side 
to  the  sunlight  for  twenty  minutes,  then  read  the 
height  of  the  mercury  in  both  instruments. 

84.  Bed  color  as  a  heat  saver.  —  Examine  a  num- 
ber of  plants  growing  in  a  deep  forest  in  the  shade. 
Many  of  those  species  which  have  large  leaves 
lying  against  the  ground,  or  floating  on  the  water, 
will  exhibit  a  layer  of  color  on  the  lower  side 
of  the  leaf  but  none  on  the  upper.  Light  which 
strikes  such  leaves  will  be  used  partly  by  the 
chlorophyl,  and  the  remainder  on  reaching  the  lower 
side  of  the  leaf  will  be  mostly  converted  into  heat 
by  the  red  pigment.  Again,  it  is  to  be  said  that  it 
is  not  definitely  known  that  the  color  is  formed  here 
for  that  purpose.  The  color  may  be  produced  as  a 
result  of  the  fact  that  it  is  subjected  to  low  tempera- 
tures at  night,  but  it  certainly  does  bear  the  above 
relation  to  light. 


THE  LEAVES  71 

85.  Hairs  as  a  2^rotectlon  to  the  leaf.  — The  leaves 
of  many  species,  especially  those  growing  in  local- 
ities subject  to  very  intense  sunlight,  are  often 
clothed  with  a  dense  layer  of  long  wavy  or  branch- 
ing hairs,  and  these  serve  to  ward  off  the  fiercer  rays 
and  prevent  drying  out.  The  same  purpose  is  also 
accomplished  by  the  development  of  a  very  heavy 
outer  cuticle  or  vvall  of  the  epidermis. 

86.  White  floivers. —  The  white  colors  of  flowers  or 
other  portions  of  the  plant  are  due  to  entirely  differ- 
ent causes.  Chief  among  these  is  the  loose  arrange- 
ment of  the  cells  and  the  absence  of  coloring  matter. 
The  air  between  the  cells  reflects  back  the  light,  giv- 
ing the  whitish  effect.  This  may  be  illustrated  by 
the  appearance  of  a  sheet  of  glass  when  unbroken, 
and  when  crushed  or  pounded  into  minute  particles. 
In  the  first  case  it  shows  its  natural  color  and  is 
transparent.  When  pounded  up  into  a  mass  of  sand- 
like particles,  the  light  is  reflected  back  from  the 
surface  of  each,  giving  the  mass  a  whitish  appear- 
ance. Test  the  paper-white  leaves  of  any  plant  you 
may  be  able  to  obtain  from  a  greenhouse  and  deter- 
mine to  what  extent  the  light  penetrates  them,  as 
in  §  73. 


72  THE  NATURE  AND    WORK  OF  PLANTS 

87.  The  positions  of  leaves.  —  Go  out  into  an  open 
woods  or  meadow  and  note  the  positions  of  the 
leaves  of  all  the  plants  you  may  see.  Select  a  suit- 
able specimen  and  walk  around  it,  noting  the  posi- 
tions of  these  organs  on  every  side  of  the  plant.  Do 
they  face  all  the  points  of  the  compass?  are  they 
horizontal  ?  Do  you  note  any  connection  between 
their  position  and  that  from  which  the  rays  of  light 
come  ?  Does  every  leaf  receive  direct  sunlight  at 
some  time  of  the  day,  and  at  the  same  hour  ? 

88.  Length  of  the  petioles.  —  Take  a  number  of 
leaves  from  different  parts  of  the  same  plant,  and 
compare  the  length  of  the  petioles.  Observe  the 
leaves  as  they  are  attached  to  the  stems.  Does  this 
inequality  of  the  petiole  serve  any  purpose  in  connec- 
tion with  the  light?  Take  the  long-petioled  leaves 
from  some  plant  and  put  them  in  the  place  of  short- 
petioled  leaves  on  another  stem.  What  is  the  result, 
so  far  as  receiving  light  is  concerned? 

89.  Leaf  mosaic.  —  A  close  examination  will  show 
that  length  of  stalk  and  size  of  blade  stand  in 
close  relation  to  each  other,  and  that  the  distance 
between  the  points  at  which  the  leaves  are  fastened 
to  the  stems  is  also  a  factor  in  their  arrangement. 


THE  LEAVES  73 

The  full  effect  of  each  factor  may  be  seen  if  the 
arrangement  of  the  leaves  of  the  ivy  or  some  plant 
which  clings  closely  to  a  wall  is  examined.  Here 
each  leaf  is  of  such  form,  size,  and  length  of  stalk 
that  it  does  not  seriously  overlap  or  shut  the  light 
from  any  of  its  neighbors. 

90.  Getting  in  the  proper  position.  —  In  addition 
to  alterations  in  the  form  and  size  of  the  stalks  and 
blades  in  order  to  get  better  exposure  to  light,  the 
protoplasm  has  the  power  of  moving  the  petiole  and 
blade  in  such  manner  that  it  will  receive  the  light  in 
the  best  manner,  or  the  one  suited  to  its  capacity. 
This  is  done  by  twisting  or  bending  the  stalk  or  peti- 
ole, or  by  bending  the  stem  to  which  it  is  attached. 

91.  Heliotropic  movements. — The  action  of  the 
leaf  or  stem  for  placing  the  blades  in  the  proper  posi- 
tion for  receiving  light  in  response  to  the  sensitive- 
ness of  the  plant  to  light  is  termed  heliotrojnsm. 
This  may  be  observed  in  house  plants  grown  by  a 
window.  Here  all  of  the  leaves  have  moved  in  such 
manner  as  to  make  their  blades  face  the  window. 
If  such  a  plant  is  turned  halfway  round  so  that  the 
leaves  face  away  from  the  window,  they  will  quickly 
regain  their  former  position.     Perform  this  experi- 


74  THE  NATURE  AND    WORK  OF  PLANTS 

ment  with  a  geranium,  and  note  the  position  of  the 
leaves  five  or  six  hours  and  a  day  later. 

Repeat  the  experiment  by  bringing  a  plant  from 
the  open  air  and  placing  it  in  a  box  with  one  small 
opening.  Sketch  the  position  of  the  stems  and 
leaves  and  do  the  same  a  day  later.  In  what  region 
has  the  movement  taken  place,  the  leaf  stalk  or  the 
stem  to  which  it  is  attached?  The  movements  of 
roots  away  from  the  light,  §  46,  are  to  be  recalled 
in  this  connection. 

92.  Movements  of  leaves  and  stems  in  response  to 
gravity.  —  Many  leaves  and  stems  are  seen  to  curve 
upward  without  regard  to  the  direction  from  which 
the  light  comes.  This  power  of  response  to  gravity 
is  termed  geotrojnsm..  It  is  this  property  of  the 
plant  which  enables  it  to  hold  its  stems  outright.  A 
different  kind  of  geotropism  makes  the  stems  of  the 
trailing  species  lie  along  the  surface  of  the  soil. 

93.  Movements  to  avoid  injury.  —  The  rays  of 
light  from  the  sun  exert  the  greatest  effect  when 
they  strike  the  surface  of  a  leaf  squarely  or  perpen- 
dicularly, as  any  one  may  know  when  he  recalls  that 
the  sun  shines  the  hottest  when  it  is  directly  over- 


THE  LEAVES  75 

head.  A  leaf  in  the  open  would  receive  the  greatest 
amount  of  light  if  it  were  held  in  a  horizontal  posi- 
tion, and  as  the  intensity  of  the  light  at  noonday  is 
such  as  to  be  injurious  to  many  species,  they  have 
developed  the  power  of  changing  the  position  of  the 
blades  at  such  times.  This  movement  generally 
consists  in  tilting,  so  that  the  tip  points  more  or  less 
directly  upward  or  downward.  In  either  case  the 
rays  of  the  noonday  sun  strike  the  surface  at  such 
an  acute  angle  that  their  effect  is  not  so  great.  The 
efficiency  of  this  device  can  be  very  readily  demon- 
strated if  you  should  place  one  tin  plate  flat  upon 
the  surface  of  the  ground,  and  stand  another  one 
upright  on  its  edge,  noting  the  difference  in  warmth 
of  the  two,  a  half  hour  later,  by  the  touch.  Move- 
ments of  the  leaves  or  leaflets  to  avoid  injury  from 
excessive  light  may  be  seen  if  the  bean,  locust,  pea, 
or  any  member  of  the  family  should  be  examined 
during  the  warmer  part  of  a  summer  day.  The 
same  plants  may  also  move  their  leaves  to  escape 
dangers  of  another  kind  during  chilly  or  cool  nights. 

94.  ComjKiss  lolants.  —  If  the  leaves  of  the  wild 
lettuce,  which  is  now  a  common  weed  in  the  United 
States,  are  examined,  it  will  be  found  that  those  on 


76  THE  NATURE  AND    WORK  OF  PLANTS 

specimens  standing  out  in  exposed  places  are  twisted 
so  that  they  point  nearly  toward  the  north  or  south 
—  a  fact  which  has  given  the  plant  its  common  name. 
The  effect  of  this  arrangement  is  to  present  the  edge 
of  the  blades  to  the  noonday  sun,  and  the  direct  rays 
may  strike  them  only  in  mid  forenoon  and  mid  after- 
noon, thus  avoiding  the  fiercer  rays  of  the  noonday 
sun.  Only  a  dozen  species  show  this  interesting 
method  of  avoiding  damage  to  the  leaves. 

95.  Some  plants  have  lost  the  poiver  of  manufac- 
turing chloroj^hyl.  —  All  species  which  take  carbon 
dioxide  from  the  air  do  so  by  means  of  the  help  of 
chlorophyl,  and  when  they  live  in  a  place  where 
they  may  get  their  food  already  formed,  the  green 
color  is  not  needed.  It  is  an  invariable  rule  with 
all  living  things,  that  as  soon  as  an  organ  or  a  struc- 
ture or  a  substance  becomes  less  useful,  the  succeed- 
ing generations  of  the  plant  do  not  perfect  the  useless 
thing.  Hence  the  species  which  have  become  able 
to  take  up  their  food  already  formed  have  lost 
their  green  color.  The  bacteria  have  all  done  so, 
as  well  as  the  mushrooms,  and  moulds,  and  their 
relatives.  A  few  flowering  species  have  undergone 
similar  changes.     If  a  plant  gets  its  food  from  the 


THE  LEAVES  77 

body  of  another  living  plant  or  animal,  it  is  termed 
a  parasite,  and  a  brief  study  has  already  been  made 
of  some  of  the  characteristics  of  species  of  this  kind 
(§  50).  If  its  food  consists  of  the  substance  of  the 
decaying  bodies  of  other  organisms,  it  is  then  termed 
a  saprophyte.  Bacteria  and  mushrooms  and  moulds 
offer  most  of  the  examples  of  both  classes. 

96.  An  association  ivithout  chlorop)liyl.  —  It  has 
been  pointed  out  in  a  previous  paragraph  that  some 
species  of  higher  plants  have  fungi  united  with  their 
roots,  forming  a  partnership  which  is  of  mutual 
benefit.  This  partnership  results  in  the  seed  plant 
securing  food  without  making  it  in  the  usual  manner, 
so  these  species  lose  their  green  color  because  of 
disuse.  The  leaves  also  decrease  greatly  in  size, 
lose  some  of  their  tissues,  and  their  characteristic 
position  with  regard  to  light.  The  Indian  pipe, 
coral  root,  pine  sap,  and  others  are  striking  illustra- 
tions of  this  action. 

97.  Fitchered  leaves.  —  Quite  a  large  number  of 
species  have  changed  their  leaves  in  such  manner 
that  they  serve  as  traps  for  catching  and  holding 
animals.  The  bodies  of  these  creatures  are  digested 
and  used  as  food.     The  greatest  variety  is  exhibited 


78  THE  NATUBE  AND    WORK  OF  PLANTS 

in  the  method  of  action.  Perhaps  those  most  easily 
found  and  examined  are  the  traps  of  the  pitcher 
plant  (Sarracenia)  and  bladderwort  {Utriciilaria). 
The  pitcher  plant  is  a  member  of  a  family  that 
extends  around  the  globe,  and  the  pitchers  of  the 
different  members  of  the  family  are  unlike ;  the  com- 
mon pitcher  plant,  or  Sarracenia,  is  found  growing 
in  bogs  and  swamps  over  a  large  part  of  the  United 
States.  A  search  should  be  made  for  them  in  such 
places,  and  fine  specimens  may  be  found  near  tama- 
rac  swamps.  They  may  be  easily  distinguished  by 
the  urn-shaped  leaves.  When  found,  note  the  man- 
ner in  which  these  leaves  arise  in  clusters  from  a 
short  underground  stem.  Note  the  general  form 
and  color  of  the  organs.  Beside  the  green,  vari- 
ous markings  of  red  and  purple  are  to  be  seen. 
Note  the  following  regions  of  the  leaf :  the  2^etiole, 
the  ^;z7cAer,  or  urn-sliaped  part,  and  the  hood,  or  lij), 
at  the  upper  outer  edge.  Split  a  leaf  from  top  to 
bottom,  noting  the  shape  of  the  cavity  and  the  con- 
tents. What  kinds  of  animals  do  you  find  inside  ? 
Next  make  an  attempt  to  determine  the  manner 
in  which  they  were  enticed  or  entrapped  in  the 
pitcher.  Examine  the  upper  and  outer  edge  of  the 
pitcher   for    honey.      Inside  and    near    the    top  of 


THE  LEAVES  79 

the  pitcher  will  be  found  a  zone  of  bristly  hairs, 
below  this  a  smooth  belt,  and  below  this  a  second 
zone  of  hairs.  Small  animals  once  descending  into 
the  pitchers  purposely  or  accidentally  are  unable  to 
make  their  way  up  again  through  the  downward 
pointed  hairs,  or  across  the  glazed  surface,  and  they 
finally  fall  into  the  liquid  in  the  bottom  of  each 
pitcher.  Glands  on  the  inner  surface  secrete  a  diges- 
tive fluid  which  dissolves  their  bodies  much  like  the 
action  of  a  stomach,  and  the  substances  may  then  be 
absorbed.  Of  course  not  all  animals  are  held  by  this 
trap.  A  winged  insect  very  rarely  escapes,  however, 
after  its  wings  are  wet  by  the  fluid.  Beside  ani- 
mals, portions  of  twigs  and  leaves  also  fall  into  the 
pitchers  and  are  more  or  less  digested  and  absorbed 
by  the  walls.  Pitchers,  in  addition  to  manufactur- 
ing food  from  the  air  by  the  aid  of  chlorophyl,  are 
seen  to  gain  another  supply  from  the  bodies  of  the 
entrapped  animals  and  plants. 

If  convenient,  the  pouched  leaves  of  the  bladder- 
wort  should  be  examined  in  the  same  manner.  This 
plant  floats  near  the  surface  of  streams  and  ponds, 
and  the  traps  may  be  seen  to  contain  a  mass  of 
dark-colored  contents  which  will  prove  to  be  the 
remains  of  small  aquatic  animals.     Some  species  of 


80  THE  NATURE  AND    WORK  OF  PLANTS 

this  plant  have  traps  large  enough  to  receive  young 
fishes,  and  they  kill  large  numbers  of  these  animals 
in  the  course  of  a  season. 

98.  Food-building  in  the  lower  forms.  —  The  leaf 
is  the  most  perfect  organ  for  the  display  of  chlo- 
rophyl  in  such  manner  as  to  make  the  best  use  of 
light,  but  in  lower  forms  it  is  done  in  a  simpler  man- 
ner. One  generation  of  the  mosses,  ferns,  and  some 
liverworts  are  furnished  with  organs  like  the  leaves 
of  seed  plants.  In  the  other  generation  the  body 
is  in  the  form  of  a  thin  plate,  or  solid  mass  of 
cells,  which  lies  flat  on  the  surface  of  the  ground. 
The  chlorophyl  in  such  cases  is  carried  in  the  upper 
layers,  where  it  may  receive  light.  The  seaweeds 
exhibit  a  great  variety  of  organs  for  this  purpose. 
Some  of  them  are  leaflike  in  general  form,  while 
others  are  massive  and  carry  chlorophyl  in  the 
outer  layers  only;  these  plants  also  carry  red  and 
blue  coloring  matter.  The  pond-scums,  which  float 
on  fresh  water,  consist  of  a  chain  of  cylindrical 
cells,  and  the  green  color  is  arranged  in  spiral  bands, 
like  corkscrews,  which  run  around  just  inside  the 
cell  wall  in  all  cells  except  the  spores.  In  still 
simpler    forms   the   chlorophyl   is   diffused   through 


THE  LEAVES  81 

the  whole  cell  and  not  set  apart  in  separate  bodies, 
as  in  the  higher  forms.  Masses  of  pond-scum,  with 
bubbles  of  oxygen  attached,  are  easily  found  in 
almost  any  pond  on  a  summer  day. 

99.  Tlie  leaf  and  loater.  —  All  of  the  food  taken 
up  by  the  roots  is  dissolved  in  one  to  ten  thousand 
times  its  weight  of  water,  and  is  carried  in  this  form 
up  through  the  stem  and  out  into  the  leaves,  where 
it  is  used  with  the  sugars  to  build  up  protoplasm  or 
make  reserve  foods.  Some  of  this  great  amount  of 
water  may  be  used  also,  but  the  greater  proportion 
is  not  needed  further,  and  since  there  is  no  method 
for  its  return  to  the  roots  it  must  be  thrown  off. 
This  must  be  done  principally  in  the  form  of  vapor. 
The  excretion  of  watery  vapor  constitutes  the  sec- 
ond important  function  of  the  leaf.  The  process  is 
termed  transpiration. 

100.  Course  of  the  ivater  in  the  leaf  —  The  water 
supply  comes  through  the  petiole,  of  course,  and 
when  it  reaches  the  lamina  it  divides  into  numerous 
streams,  each  one  of  which  follows  a  nerve  or  rib 
and  goes  out  into  all  of  its  branches.  This  may 
be  demonstrated  if  a  leaf  of  the  maple  or  poplar  is 
cut  from  the  stem  of  a  living  tree,  and  the  base  of 


82  THE  NATURE  AND    WORK  OF  PLANTS 

the  petiole  inserted  in  a  bottle  of  red  ink  or  aniline 
in  water.  Examine  a  day  later.  The  color  will 
have  marked  out  the  conducting  system  of  the  leaf. 
This  will  be  found  to  distribute  the  liquid  to  the 
remotest  and  smallest  parts  of  the  lamina. 

101.  Transpiration.  —  Clustered  around  the  con- 
ducting tubes  are  the  soft,  thin-walled  mesojjhyl 
cells,  which  draw  water  from  the  veins.  The  liquid 
is  constantly  evaporated  from  the  walls  of  these  cells 
into  the  air  between  them,  and  this  connects  with 
the  outer  air  by  means  of  the  thousands  of  minute 
openings  in  the  lower  side  of  the  leaf.  The  sun 
shines  on  the  upper  side  of  the  leaf,  heating  it  and 
the  delicate  cells  underneath,  and  they  constantly 
evaporate  water  into  the  air  spaces,  and  this  air  laden 
with  water  pours  out  of  the  stomata  and  is  replaced 
by  drier  air  from  the  outside. 

102.  Tlie  vapor  transp)ired. — That  watery  vapor 
is  thrown  off  by  the  leaf  may  be  shown  if  the  petiole 
of  a  leaf  is  passed  through  a  small  hole  in  a  large 
piece  of  cardboard  and  immersed  in  a  tumbler  of 
water.  Put  clay  or  wax  around  the  petiole  to  pre- 
vent any  water  vapor  from  coming  up  in  this  way 
through  the  hole  in  the  cardboard.     Now  invert  a 


THE  LEAVES  83 

second  tumbler  over  the  blade.  Examine  a  few 
hours  later.  The  vapor  thrown  off  by  the  leaf  will 
have  collected  in  the  form  of  small  drops  on  the 
inside  of  the  second  tumbler. 

103.  Measurement  of  the  amount  of  ivater  tliroion 
off  by  a  plant.  — Lay  a  piece  of  oiled  cloth  18  inches 
square  on  the  table,  and  in  the  centre  set  a  potted 
geranium  or  tomato.  Bring  the  edges  of  the  cloth 
up  around  the  pot  and  tie  closely  around  the  base  of 
the  stem.  Water  can  now  evaporate  from  the  plant 
only.  Set  on  one  pan  of  a  grocer's  scale  and  place 
weights  in  the  other  pan  until  it  balances. 

If  a  scale  is  not  to  be  had,  suspend  a  wooden  rod 
by  the  middle  and  to  each  end  tie  a  small  bucket. 
Place  the  plant  in  one  and  weights  in  the  other. 
Examine  a  few  hours  later.  The  plant  will  have 
grown  lighter.  Remove  weights  from  the  opposite 
end  of  the  beam  until  the  balance  is  restored.  How 
much  weight  has  been  taken  out  ?  This  represents 
the  amount  of  the  water  thrown  off  by  the  plant. 

104.  Sunlight  increases  transinration.  —  Repeat 
this  experiment  in  the  sunlight  and  compare  the 
amount  of  water  lost  with  that  of  the  previous 
experience. 


84  THE  NATURE  AND   WORK  OF  PLANTS 

105.  Regulation  and  control  of  transpiration. — 
The  leaf  is  able  to  control  the  amount  of  water 
given  off  by  opening  and  closing  the  stomata.  The 
amount  of  moisture  already  in  the  air  influences 
the  transpiration  greatly,  and  as  this  amount  varies 
widely  in  different  places  tliere  are  a  large  number 
of  forms  of  leaves  adapted  to  the  different  conditions. 
The  leaf  may  shield  itself  from  the  drying  effects  of 
intense  sunlight  by  heavy  cuticles,  coats  of  hair,  or 
wax,  or  by  the  upright  positions  described  in  §  93. 

106.  Wax  or  hloo7n  as  a  means  of  prevention  of 
excessive  loss  of  water.  —  Select  some  leaf  which  has 
the  surfaces  covered  with  a  whitish  hloom  (cabbage). 
Kub  the  bloom  from  one  and  place  it  by  the  side  of  a 
second  which  has  been  handled  carefully  in  order  not 
to  disturb  the  bloom.  Which  is  the  more  wilted  in 
two  or  three  hours  ?  The  best  results  will  be  obtained 
if  the  leaves  are  placed  in  the  sunlight. 

107.  Size  of  leaves  and  dryness  of  the  air.  —  Spe- 
cies growing  in  dry  air  generally  exhibit  very  small 
leaves,  while  those  living  in  wet  places  or  where  the 
air  is  very  damp  develop  large  laminae.  It  is  neces- 
sary to  have  a  stream  of  water  constantly  travelling 
from  the  roots  to  the  leaves,  and  plants  living  in 


THE  LEAVES  85 

very  damp  or  rainy  situations  secure  this  stream  by 
building  very  large  leaves.  The  banana  is  a  com- 
mon example,  and  many  other  tropical  plants  show 
leaves  several  times  as  large. 

108.  Sleep  movements. — If  the  position  of  the 
leaflets  of  the  bean  or  locust  are  noticed  at  sunset  or 
later,  it  will  be  seen  that  their  blades  are  placed 
nearly  vertically.  This  position  is  supposed  to  be  a 
method  of  preventing  the  leaf  from  cooling  so  rapidly 
as  it  would  if  held  horizontal,  and  also  from  accumu- 
lating a  layer  of  dew  which  would  hinder  transpira- 
tion.    (See  also  §  93.) 

109.  Velvety  surfaces.  —  If  the  leaves  of  some  of 
the  species  of  begonias  are  examined,  they  will  be 
found  to  show  an  upper  surface  that  is  velvety  to 
the  touch,  and  when  examined  with  a  hand  lens 
appear  to  have  an  immense  number  of  small  pro- 
jections. This  is  due  to  the  fact  that  the  cells  of  the 
upper  side  of  the  leaf  are  all  extended  in  little  cones. 
The  cones  entrap  the  rays  of  sunlight  as  it  were,  and 
refract  them  so  that  they  warm  the  leaf  and  increase 
the*  transpiration  over  what  it  would  be  if  the  surface 
were  smooth.  This  device  is  also  exhibited  by  the 
petals  of  violets,  pansies,  and  primulas. 


86  THE  NATURE  AND   WORK  OF  PLANTS 

110.  Autumnal  leaf  fall.  —  The  greater  number 
of  the  hardy  or  long-lived  plants  of  the  United  States 
are  deciduous,  or  drop  their  leaves  every  year.  This 
casting  of  the  leaves  is  one  of  the  distinctive  features 
of  the  close  of  the  growing  season.  It  is  popularly 
supposed  to  be  due  to  the  action  of  cold,  but  this  is 
a  mistake.  The  leaves  of  a  large  tree  throw  off  as 
much  as  a  barrel  of  water  in  the  course  of  a  day,  and 
when  the  plant  finds  that  it  is  losing  water  in  the 
dry  August  days  faster  than  it  can  take  it  up  from 
the  soil,  it  begins  to  get  rid  of  the  organs  which  use 
most  of  it. 

111.  Separatory  layer.  —  In  order  to  be  able  to 
cut  off  the  leaf  quickly  and  economically,  a  ring  of 
tissue  is  formed  at  the  base  of  the  stalk,  w^hich 
spreads  the  other  tissues  apart  as  it  grows.  After 
this  sejjarating  layer  is  fully  formed  it  is  very  brittle, 
and  the  slightest  breath  of  wind  will  split  it  apart 
and  allow  the  leaf  to  fall  to  the  ground.  In  com- 
pound leaves,  such  as  the  horse-chestnut,  separatory 
layers  are  formed  at  the  base  of  each  leaflet  also,  and 
in  some  ivies  a  piece  of  the  branch  is  cut  off  with  the 
leaf. 

If  a  twig  of  maple  with  the  attached  leaf  is  taken 


THE  LEAVES  87 

from  the  tree  in  September,  caiid  a  slicing  cut  is  made 
through  the  base  of  the  petiole  and  the  twig,  the 
separatory  layer  may  then  be  seen  with  a  magnify- 
ing glass.  Trees  which  usually  shed  their  leaves 
are  sometimes  seen  to  retain  them  during  the  winter. 
This  is  usually  due  to  the  fact  that  the  formation  of 
the  separatory  layer  has  been  interrupted  by  cold  or 
drought. 

112.  The  length  of  life  of  leaves.  —  The  leaves 
of  the  conifers  and  other  evergreen  trees  may  remain 
in  place  on  the  branches  two  or  three  years,  or  even 
longer.  After  a  time,  however,  they  become  dam- 
aged by  the  wind,  and  by  insects  or  other  agencies, 
and  are  cast  off.  An  evergreen  tree  is  casting  its 
leaves  almost  continually,  but  as  it  loses  but  a  few 
at  a  time  it  is  not  noticeable.  Quite  a  deep  layer  of 
needles  ma-y  be  found  underneath  almost  any  pine 
tree. 

113.  Groivth  of  leaves.  —  The  greatest  variation  is 
shown  in  the  method  and  rapidity  of  growth.  All 
parts  of  the  organ  do  not  grow  with  equal  rapidity, 
as  may  be  seen  by  the  following  test :  Mark  off 
intervals  with  India  ink  on  the  petioles  and  midribs 
of  leaves  of  sunflowers,  narcissus,  and  any  other  con- 


88  THE  NATURE  AND    WORK  OF  PLANTS 

venient  species.  Measure  from  day  to  day  and  find 
the  total  increase  in  length,  and  note  the  region  of 
greatest  growth.  In  general,  it  will  be  found  that 
grasslike  leaves  grow  at  the  base,  while  others 
extend  chiefly  by  the  development  of  the  terminal 
portion. 

114.  Wilting.  —  If  the  leaf  of  any  rapidly  growing 
plant  is  taken  off  and  laid  in  the  sun  for  an  hour, 
it  may  be  seen  that  it  becomes  limp  and  is  said  to  be 
ivilted.  Compare  with  a  fresh  leaf.  It  is  quite  flexi- 
ble, and  the  soft  tissues  between  the  ribs  appear  to 
be  shrunken.  Hold  an  end  of  the  leaf  in  either  hand 
and  pull  until  it  breaks  in  two  parts.  Repeat  with 
a  fresh  leaf.  The  wilted  leaf  is  as  strong  in  this 
way  as  the  fresh  one.  It  has  not  lost  any  of  its 
mechanical  tissues,  and  its  limpness  must  be  due  to 
the  loss  of  water.  The  cells  of  fresh  leaves  of  the 
plant  are  filled  with  water  to  such  extent  that 
they  are  stretched  and  the  walls  are  very  firm,  in 
the  same  manner  that  the  string  of  a  bow  is  as  rigid 
as  a  bar  of  iron  when  the  bow  is  prepared  for  use, 
but  quite  limp  and  flexible  when  separate. 

At  noonday  in  midsummer  and  at  other  times  the 
leaves  do  not  receive  as  much  water  as  they  evapo- 


THE  LEAVES  89 

rate,  and  as  a  consequence  they  wilt  more  or  less. 
The  wiltmg  is  itself  a  protection  against  serious  in- 
jury, for  in  this  condition  the  openings  on  the  lower 
surface  of  the  leaf  are  closed,  and  the  drooping  posi- 
tion assumed  by  the  blade  operates  to  diminish  the 
amount  of  water  thrown  off  into  the  air. 

115.  Transplanting  trees  and  herhs  is  attended 
by  wilting.  —  A  plant  usually  develops  a  system  of 
roots  with  hairs  capable  of  supplying  the  necessary 
amount  of  moisture  to  the  leaves,  and  when  it  is 
lifted  from  the  ground  the  process  is  attended  with 
more  or  less  damage  to  the  roots  or  hairs.  When 
the  plant  is  set  in  a  new  position  its  absorbing  pow- 
ers are  not  so  great  as  before,  and  if  it  is  allowed  to 
retain  all  of  its  leaves,  it  will  throw  olf  more  water 
than  it  receives,  and  wilting  will  result.  To  avoid 
this  the  branches  are  trimmed  in  such  manner  as  to 
reduce  the  evaporating  surface  to  the  proper  propor- 
tion to  the  roots.  One  may  see  nurserymen  putting 
out  trees,  the  tops  of  which  have  been  trimmed  to 
bare  poles. 

116.  Freezing  or  frosting.  —  An  observation  of 
the  plants  growing  in  the  open  air  after  the  first 
frost  of  autumn  will  show  that  the  leaves  of  some 


90  THE  NATURE  AND    WORK  OF  PLANTS 

species  are  quite  blackened  and  shrivelled,  while 
others  still  appear  bright  and  green  and  remain  so 
until  the  actual  approach  of  winter  and  many  frosts 
have  been  endured.  This  leads  at  once  to  the  con- 
clusion that  separate  species  have  different  powers  of 
resistance  to  cold. 

It  is  seen  at  once  that  a  temperature  sufficient  to 
freeze  water  does  not  kill  all  species.  Then  again 
some  species,  such  as  the  melons,  coleus,  tobacco,  and 
tropical  plants  are  killed  by  temperatures  of  two 
degrees  above  the  freezing  point.  Apple  leaves  are 
killed  by  a  temperature  of  two  to  six  degrees  below 
the  freezing  point,  cabbage  five  to  seventeen  be- 
low, peaches  two  or  three  below,  tomatoes  one  below, 
wheat  one  below,  strawberries  two  to  four  below, 
while  the  grasses  of  the  Arctic  regions  endure  temper- 
atures of  eighty  and  ninety  below  the  freezing  point. 

The  water  in  some  species  may  be  frozen  without 
damage  to  the  protoplasm,  but  if  the  frozen  speci- 
mens are  brought  into  a  warm  room  and  thawed 
quickly,  the  shock  of  the  sudden  change  will  kill 
them.  It  is  for  this  reason  that  frozen  specimens 
may  be  sometimes  thawed  without  damage  in  water. 
The  use  of  the  water  also  prevents  the  specimen 
from  drying  out. 


THE  LEAVES  91 

117.  The  air  is  colder  on  a  frosty  night  near  the 
ground  than  it  is  a  few  feet  above  it.  —  If  one  ther- 
mometer is  hung  near  the  surface  of  the  ground  on 
a  quiet  night  in  mid  autumn,  and  another  ten  to 
twenty-five  feet  higher  in  the  branches  of  a  tree, 
it  will  be  found  that  it  may  be  five  to  ten  degrees 
colder  near  the  ground  than  it  is  in  the  tree  tops. 
This  is  due  to  the  fact  that  the  soil  cools  very 
rapidly,  and  the  layer  of  air  resting  on  it  is  also 
cooled,  while  the  upper  air  is  comparatively  warm. 
On  account  of  this  fact  the  leaves  and  buds  on  the 
lower  branches  of  a  tree  may  be  frosted,  while  those 
on  the  upper  part  are  untouched.  The  low-growing 
shrubs  and  herbs  will  be  frosted  before  the  taller 
trees.  If,  however,  a  great  movement  of  wind  from 
the  northward  covers  the  country  with  cold  air,  it 
will  result  in  a  general  freeze  which  affects  all  alike. 
The  farmer  and  the  fruit  raiser  prevent  damage  to 
their  crops  from  frosts  by  covering  the  plants  with  a 
shield  which  will  prevent  the  loss  of  heat  by  the 
ground  and  by  the  plants,  by  building  fires  to  heat 
up  the  layer  of  cold  air,  or  by  making  smudge  fires 
which  add  heat,  smoke,  and  moisture  to  the  air, 
making  a  fog  blanket  that  prevents  the  loss  of  heat 
as  effectually  as  a  covering   of  cloth  might  do  it. 


92  THE  NATURE  AND   WORK  OF  PLANTS 

None  of  these  devices  may  protect  against  freezing 
in  general  cold  weather. 

118.  Drainage  of  cold  air.  —  The  layer  of  cold 
air  on  the  surface  of  the  soil  is  heavier  than  the 
warm  air  above  it,  and  in  rough  or  broken  country 
this  heavier  air  flows  down  hill  as  water  would, 
accumulating  in  the  valleys,  w^hich  thus  become  very 
much  colder  than  the  hill-tops  around  them.  The 
temperature  of  the  valleys  is  often  ten  to  twenty 
degrees  lower  than  that  of  the  hills  near  by.  As  a 
consequence  of  this  fact,  vineyards,  orchards,  and 
gardens,  in  which  delicate  varieties  are  cultivated, 
are  planted  on  ridges  and  hills  in  preference  to 
low-lying  valleys. 


VI.   STEMS 

119.  The  nature  of  stems.  —  The  stem  is  the 
main  axis,  or  central  member  of  the  body  of  the 
plant.  From  its  lower  end  the  roots  arise  and  pene- 
trate the  soil,  while  leaves  and  reproductive  organs 
are  borne  on  its  upper  part.  Stems  are  often  de- 
scribed as  springing  from  roots,  when  they  grow 
from  underground  stems.  This  is  a  mistake,  except 
in  a  very  few  instances  in  which  roots  are  capable  of 
giving  rise  to  stems. 

It  is  necessary  that  the  roots  should  be  buried  in 
the  soil  for  the  purpose  of  absorbing  food,  and  that 
the  leaves  should  be  held  up  in  the  sunlight  to 
enable  them  to  form  food ;  also  that  the  reproduc- 
tive organs  should  be  held  in .  a  position  that  will 
enable  them  to  perpetuate  the  species.  This  means 
that  the  roots  on  one  hand  and  the  leaves  and  flow- 
ers on  the  other  may  be  separated  by  some  distance. 
The  stem  is  the  connecting  member,  and  its  bulk  and 
length  will  vary  with  the  habits  and  needs  of  the 
separate  species. 


94  THE  NATURE  AND    WOBK  OF  PLANTS 

120.  Stems  are  made  up  of  sections,  or  internodes. 

—  If  the  stem  of  a  mint  or  of  the  corn  is  examined, 
it  will  be  found  that  it  exhibits  a  number  of 
"joints,"  indicated  by  external  ridges  which  divide 
it  into  a  number  of  sections.  Take  two  sections  of 
the  stem  not  adjoining,  and  compare  them.  No  dif- 
ference will  be  found  except  in  the  matter  of  size 
and  age.  The  arrangement  of  the  tissues  is  identi- 
cal. Repetition  of  this  test  will  show  that  a  stem  is 
made  up  of  a  number  of  sections  of  the  same  struc- 
ture. This  characteristic  is  one  which  is  not  found 
in  any  other  member  of  the  plant. 

121.  Branches  arise  at    the  nodes  or  joints  only. 

—  The  branches  of  roots  were  seen  to  arise  at 
any  point  on  'the  main  root.  Leaves,  branches, 
and  flowers  are  seen  to  be  given  off  at  the 
nodes  only  of  stems.  Roots  emerge  from  the  ex- 
treme lower  end  of  the  stem,  or  they  may  arise 
from  the  lower  nodes,  as  in  the  case  of  the  stilt  or 
prop  roots  of  the  corn,  or  from  any  part  of  the  stem 
in  climbing  species. 

122.  Relation  of  the  leaves  and  branches.  —  It 
may  be  seen  that  buds  or  branches  arise  from  the 
stem  immediately  above  the  point  at  which  a  petiole 


STEMS  95 

is  attached,  that  is,  in  the  axil  of  the  leaf.  While 
this  is  generally  the  case,  yet  many  species  give  off 
branches  just  below  the  leaf.  Wherever  a  branch  is 
seen  on  a  stem,  one  may  be  certain  that  it  arose 
originally  just  above  or  below  a  leaf.  The  leaf  has 
fallen  off,  and  the  branch  has  continued  to  grow  and 
enlarge  until  all  trace  of  the  leaf  is  lost. 

123.  Leaf  traces. — When  the  leaf  falls  from 
the  stem  its  petiole  is  cut  off  cleanly  by  means  of 
the  separatory  layer  described  in  a  previous  para- 
graph. The  scar  is  noticeable  for  some  time,  and 
may  be  seen  very  plainly  on  the  twigs  of  the  maple, 
oak,  or  chestnut,  or  on  the  vine  of  the  grape. 

124.  Relation  of  leaves  and  floivers.  —  Flower 
stalks  are  also  seen  to  arise  from  the  axils  of  leaves. 
A  single  flower  on  its  own  stalk  may  arise  from  the 
axil  of  the  leaf  without  changing  the  character  or 
the  size  of  the  latter  in  any  way.  When  a  branch 
bears  a  great  number  of  flowers  closely  crowded 
together,  like  the  lobelia,  the  mints,  mullein,  and 
larkspur,  the  leaves  at  the  basis  of  the  numerous 
flower  stalks  are  much  smaller  than  those  on  other 
parts  of  the  stem,  and  are  scarcely  more  than  little 
wedges  of  green  tissue  which  are  termed  bracts. 


96  THE  NATURE  AND   WORK  OF  PLANTS 

125.  Structure  of  stems.  —  If  a  small  branch  of 
the  elm,  beech,  maple,  or  chestnut  is  cut  off  and  then 
a  portion  of  the  branch  is  split  lengthwise,  it  may  be 
seen  that  a  hard  covering  of  bark  encloses  the  whole. 
Immediately  inside  this  is  a  layer  of  soft  tissue  of 
material  easily  crushed  and  full  of  water.  This 
material  is  living  while  the  bark  was  chiefly  made  up 
of  dead  tissues.  Small  extensions  of  the  living  tissue 
penetrate  the  wood  which'  occupies  the  greater  part 
of  the  volume  of  the  branch.  In  the  centre  is  to  be 
seen  a  small  amount  of  soft  pith,  which  may  easily  be 
cut  or  torn,  and  is  generally  made  up  of  dead  cells  in 
older  branches.  The  branch  is  thus  seen  to  be  com- 
posed of  living  and  dead  cells,  and  the  dead  tissue 
greatly  exceeds  the  living  in  bulk. 

126.  Uses  of  stems.  —  The  purpose  of  the  stem 
is  twofold :  to  hold  up  the  leaves  and  flowers,  and 
to  conduct  water  and  food  between  the  leaves  and 
roots.  The  method  by  which  these  functions  are 
carried  out  may  be  best  understood  after  a  study 
of  the  scheme  in  which  the  tissues  are  arranged  in 
the  stem.  This  has  been  seen  roughly  in  the  branch 
of  the  tree  examined,  but  it  will  be  necessary  to  see 
the  manner  in  which  the  different  parts  of  the  living 


STEMS  97 

and  dead  tissues  are   disposed  with  regard  to  each 
other. 


127.  Methods  hy  ivhich  firmness  is  secured.  —  If 
the  stem  is  to  hold  the  leaves  and  flowers  aloft, 
it  must  secure  a  certain  amount  of  rigidity  in  its 
own  body.  It  does  this  by  two  methods,  which 
may  be  illustrated  as  follows  :  Cut  off  a  fresh  branch 
from  a  woody  tree,  and  also  the  stem  of  a  tomato  or 
potato,  ajad  lay  in  the  hot  sun  for  two  hours.  Take 
a  second  fresh  branch  from  the  tree  and  bend  or 
break  it  across  the  knee.  Bend  or  break  the  one 
which  has  lain  in  the  sun  in  the  same  manner.  Has 
the  latter  lost  any  of  its  rigidity  or  firmness  ?  Is  it 
more  easily  bent  ?  Repeat  with  other  stems.  What 
is  the  result  ?  It  will  doubtless  be  found  that  the 
herbaceous  stem  has  lost  its  firmness  and  that  it  is 
wilted  and  may  be  very  easily  bent  double,  while  the 
ivoody  stem  is  practically  unchanged.  Both  stems 
lost  water  in  the  sun.  This  did  not  affect  the  woody 
stem,  but  did  the  other.  It  seems  fair  to  conclude 
that  the  presence  of  water  is  necessary  for  the  firm- 
ness of  herbaceous  stems,  and  it  is  not  for  the  woody 
stems.  If  the  experiment  is  carried  farther,  it  will 
be   found   that   dead    and    thoroughly   dried    stems 


98  THE  NATUEE  AND   WORK  OF  PLANTS 

are  more  rigid  than  the  living  members.  This  is 
due  to  the  fact  that  even  the  soft  living  tissues 
become  hard  when  dead  and  dry. 

Stems  secure  firmness  by  the  presence  of  hard 
mechanical  tissues  and  by  filling  soft  tissues  full  of 
water  under  pressure,  as  in  leaves. 

128.  Arrangement  of  hard  or  dead  cells  to  secure 
firmness  of  stems.  —  The  dead  cells  of  stems  are 
arranged  in  the  form  of  strands  or  girders  after  the 
principles  used  by  an  engineer  or  architect  in  con- 
structing a  tower  or  tall  building.  The  architect 
uses  wood,  brick,  cement,  and  metal  as  material 
from  which  to  construct  the  tower.  The  plant  uses 
loood,  hast,  which  resembles  cable  or  wire  rope  in  its 
properties  and  is  as  strong  as  wrought-iron,  col- 
lenchyma,  which  is  elastic,  and  also  soft  ^:>z7/i  cells. 
The  properties  of  wood  are  too  well  known  to  need 
discussion.  Bast  cells  make  up  the  fibres  which  are 
taken  from  the  flax  plant  and  used  by  man,  and  col- 
lenchyma  forms  the  sharp  angles  of  the  stems  of  the 
mints  and  is  very  much  like  cartilage  or  rubber.  The 
plant  has  thus  rigid  beams,  flexible  cables,  and  soft 
spongelike  filling  or  cement  for  its  building  mate- 
rials,  and   the  towers  it   constructs  are  greater   in 


STEMS  99 

height  in  proportion  to  tliickness,  and  show  greater 
strength  and  efficiency,  than  those  built  by  man. 

129.  Arrangement  of  mechanical  tissues  iti  a 
stem  of  a  grass.  —  Secure  an  uninjured  cornstalk. 
Take  out  a  single  internode,  or  the  part  between 
two  joints,  and  dissect  it.  Note  the  hard  plates 
which  extend  entirely  through  the  stem  at  the  nodes. 
The  outer  layer  is  in  the  form  of  a  cylinder  and  is 
hard  and  rigid.  Cut  in  two  parts  lengthwise.  The 
interior  is  filled  with  the  soft  pith.  In  this  pith 
are  great  numbers  of  strands  and  fibres  which  run 
from  the  plate  at  one  end  to  the  other.  Now  split 
the  entire  piece  into  small  strips,  and  without  injur- 
ing any  of  the  separate  parts  tie  them  together  in 
a  bundle.  Lay  the  bundle  on  a  table  with  half  of 
its  length  projecting  over  the  edge.  Weight  down 
the  end  on  the  table.  Now  tie  weights  to  the  other 
end  and  determine  the  amount  necessary  to  break 
the  bundle  of  building  material.  Repeat  the  opera- 
tion with  a  section  of  the  stem  which  has  not  been 
dissected.  It  will  doubtless  be  seen  that  the  mate- 
rials themselves  are  not  very  strong,  but  when  fitted 
together  in  proper  form  they  make  an  extremely 
rigid   stem. 


100  THE  NATURE  AND    WORK  OF  PLANTS 

The  cornstalk  is  seen  to  be  a  cylindrical  tower, 
many  storeys  in  height.  Each  storey  is  filled  with 
the  cementing  pith,  and  numerous  braces  run  from 
the  ceiling  to  the  floor  of  each  in  a  method  that 
could  not  be  improved  by  the  best  engineer. 

130.  Mechanical  tissues  in  a  sunflower  stem. — 
Repeat  the  above  experiment  with  the  stem  of  the 
sunflower.  Cut  across  a  young  stem  and  note  the 
position  of  the  building  elements.  A  few  strands  of 
wood  will  be  found  arranged  in  a  circle,  and  on  the 
outer  side  of  each  bundle  of  wood  is  a  bundle  of 
bast.     The  centre  of  the  stem  is  filled  with  pith. 

131.  Mechanical  tissues  in  a  carnation  stem. — 
Repeat  the  tests  of  strength  with  a  carnation  stem. 
Cut  a  stem  length-  and  cross-wise  and  note  the 
manner  in  which  the  material  is  arranged.  The 
bast  will  be  found  to  form  a  circle,  and  immediately 
attached  to  the  inside  of  this  circle  is  a  second  circle 
of  wood.  The  centre  is  filled  with  pith.  This  stem 
is  then  like  a  tower  made  of  two  strong  tubes 
fastened  together,  and  the  centre  is  filled  with  the 
cementing  pith,  which  is  also  living  and  which  be- 
comes firm  and  bracing  by  the  absorption  of  water. 
Examine  the  stem  of  a  mint  in  the  same  manner. 


STEMS   '  101 

132.  Arrangement  of  rtieclianical  tissues  in  a 
petiole.  —  The  types  of  stems  described  above  stand 
erect  and  support  the  weight  of  the  leaves  like  a 
pillar,  and  the  bending  force  of  the  wind  like  a 
tower.  The  petioles  of  leaves  generally  hold  the 
blade  in  a  horizontal  position,  and  the  weight  acts 
always  to  bend  the  petiole  in  one  direction,  down- 
ward. To  meet  this  strain  it  is  necessary  to  have 
the  building  material  arranged  in  a  half  circle,  as 
may  be  seen  if  the  leaf  of  the  maple  or  chestnut  is 
examined. 

133.  TJie  firmness  of  plants  that  "become  limp 
when  dried.  —  Select  a  young  stem  of  any  plant  which 
would  become  limp  if  you  laid  it  in  the  sun.  The 
tips  of  elder  stems  in  April  or  May  will  offer  splendid 
material.  Cut  away  from  opposite  sides  of  the  stem 
until  only  a  thin  strip  remains,  which  includes  the 
central  part  of  the  stem.  Now  divide  this  exactly 
down  the  middle  with  a  sharp  knife.  This  will 
make  two  sheets  of  material,  each  of  which  is  com- 
posed of  a  strip  of  living  pith  full  of  water  under 
pressure,  and  the  wood  which  will  bend  but  not 
stretch.  After  a  few  minutes  place  the  two  strips 
together  in   their  original   position.     What  changes 


102  THE  NATURE  AND    WORK  OF  PLANTS 

of  form  have  they  undergone  ?  Cut  the  stalks  of 
the  calla  lily  or  rhubarb  into  strips,  and  note  be- 
havior. 

134.  Stems  as  conducting  organs.  —  The  position 
of  the  stem  between  the  leaves  where  sugars  and 
other  substances  are  manufactured  and  the  roots 
where  water  and  mineral  salts  are  taken  up  makes 
it  necessary  for  it  to  conduct  the  products  of  the 
leaf  downward,  and  the  materials  taken  up  by  the 
leaf  upward.  There  is  a  stream  of  water  upward 
and  a  stream  of  food  material  downward,  but  the 
two  are  not  connected,  and  there  is  nothing  like  a 
circulation  of  the  sap. 

135.  Upward  path  of  sajJ.  —  Cut  off  a  stem  of 
the  tomato  or  touch-me-not  with  a  number  of  sound 
leaves  attached,  and  thrust  the  lower  end  of  the 
stem  into  a  bottle  of  red  ink  or  a  tumbler  of  water 
colored  with  aniline  dye.  After  four  or  five  hours 
remove  and  dissect  the  stem.  What  portions  are 
colored  ?  This  will  show  through  what  tissues  the 
liquid  has  passed.  It  is  to  be  seen  that  the  dead 
wood  cells  also  serve  as  conduits  for  water  in  addi- 
tion to  their  function  of  making  the  stem  rigid. 


STEMS  103 

136.  Fath  of  sap  in  large  trees.  —  Each  year  a 
new  layer  of  wood  is  added  to  the  trunk  of  a  tree, 
thus  increasing  its  thickness  by  the  small  part  of  an 
inch.  If  the  previous  experiment  might  be  repeated 
with  a  large  tree,  it  would  be  found  that  only  the 
outer  layers  of  wood  in  the  trunk  would  be  colored, 
showing  that  it  is  through  these  only  that  the  sap 
ascends. 

137.  Girdling.  —  An  interesting  fact  in  this  con- 
nection is  the  behavior  of  a  tree  when  girdled. 
•Girdling  is  usually  done  by  removing  the  bark, 
the  living  layer,  and  some  of  the  outer  wood  of  the 
trunk,  and  is  done  for  the  purpose  of  killing  the 
tree.  In  most  species  the  removal  of  the  outer 
layer  of  wood  cuts  off  the  conduits  which  carry  the 
water  to  the  leaves,  and  if  it  is  done  in  the  spring, 
the  tree  generally  dies  the  following  summer.  Some 
are  able  to  send  water  up  through  the  inner  layers, 
and  not  only  live  that  year  but  the  following  year 
also.  A  few  instances  have  been  found  in  which  the 
tree  has  survived  the  operation  many  years. 

138.  Doivmvard  path  of  material  from  the  leaf. — 
Trees  which  live  through  one  summer  but  die  at  the 
beginning  of  the  next,  are  injured  by  starvation  of 


104  THE  NATURE  AND   WORK  OF  PLANTS 

the  roots.  These  organs  are  constantly  receiving 
material  from  the  leaves,  but  have  a  surplus  on  hand 
almost  all  of  the  time,  and  some  is  also  to  be  found 
in  the  lower  part  of  the  stem.  During  the  first  year 
this  is  sufficient  for  their  nourishment,  but  it  is  gen- 
erally exhausted  before  the  beginning  of  the  next 
season.  This  material  passes  down  very  slowly 
through  the  layer  of  living  tissue  immediately  under- 
neath the  bark,  and  its  flow  is  interrupted  in  any 
girdling  operation.  If  the  tree  lives  several  years 
after  girdling,  it  may  be  supposed  that  its  roots  have 
formed  partnership  with  fungi  in  such  manner  that 
it  receives  its  food  from  them  (see  §  52).  As  a  mat- 
ter of  fact  the  stumps  of  many  of  the  coniferous 
trees  are  known  to  live  for  long  periods,  perhaps  a 
decade,  by  means  of  food  obtained  in  this  manner. 

Girdling  of  branches  is  used  as  a  method  of 
increasing  the  size  and  quality  of  fruit  borne  on 
them. 

139.  Forces  ivhich  carry  the  sap  upioard  through 
the  stem.  —  Information  upon  the  forces  which  pump 
water  up  to  the  top  of  tall  trees  is  very  incomplete. 
It  is  quite  certain  that  it  needs  as  much  power  to 
carry  water  to  the  top  of  a  tree  a  hundred  feet  high 


STEMS  105 

as  it  does  to  send  it  up  through  an  iron  pipe  to  the 
same  distance.  As  a  matter  of  fact  it  takes  more 
force  to  carry  it  up  in  the  tree  because  it  must  pass 
through  such  very  small  vessels.  While  the  whole 
process  may  not  be  fully  understood,  yet  some  fea- 
tures of  it  may  be  illustrated  in  the  following 
paragraphs. 

140.  Boot  or  Needing  pressure.  —  If  the  stump 
of  a  tree  which  has  been  cut  down  in  the  spring  is 
examined  it  will  be  seen  that  the  sap  is  oozing  from 
the  cut  surface  in  great  volume,  and  if  a  cup  is 
placed  under  the  cut  end  of  a  grapevine  at  this 
season  the  amount  of  liquid  thrown  out  may  be 
measured.  This  bleeding  is  due  to  a  pressure  exerted 
by  the  living  cells  of  the  stem  and  roots,  and  it  is 
sufficient  to  force  water  to  the  tops  of  small  plants 
like  the  sunflower  in  the  temperate  zone  and  in  trees 
in  the  tropics,  but  in  the  United  States  it  could  not 
send  sap  to  the  leaves  of  large  trees.  Then,  again, 
root  pressure  is  strong  only  in  early  spring. 

141.  The  floiv  of  sap  of  the  sugar  maple.  —  Not 
all  flow  of  sap  is  due  to  bleeding  pressure.  Sugar 
maples  are  tapped  to  obtain  the  sweet  sap  at  a  time 
in  the  spring  when  the  ground  is  still  frozen.     The 


106  THE  NATURE  AND    WORK  OF  PLANTS 

flow  is  due  in  part  to  the  effect  of  the  sun's  rays 
upon  the  trunk,  heating  and  expanding  the  liquids 
and  gases  in  it,  and  driving  the  sap  out  the  auger 
hole  in  this  way.  After  the  ground  thaws  out  the 
sap  ceases  to  flow  in  quantity. 

The  sugar  obtained  from  the  sap  has  been  stored 
up  in  the  pith  cells  in  the  rays  of  the  wood  during 
the  winter. 

142.  JDeiv.  —  The  sparkling  gems  of  dew  which 
make  a  lawn  so  beautiful  of  a  summer  morning  are 
not  usually  formed  from  the  air,  but  are  drops  of 
water  which  have  been  forced  up  through  the  leaves 
by  the  root  pressure.  During  the  warm  and  sunny 
part  of  the  day  the  water  is  thrown  off  by  the  leaf 
as  fast  as  it  may  be  received  from  the  roots,  but  at 
night  the  air  is  cool  and  moist,  and  it  is  not  able  to 
do  so.  As  a  consequence,  the  liquid  is  forced  up  until 
it  fills  the  spaces  in  the  leaf  and  finally  oozes  out 
through  slits  in  the  epidermis.  Of  course  dew  may 
be  formed  by  the  condensation  of  moisture  from  the 
atmosphere,  but  that  on  grass  usually  comes  up  from 
the  roots. 

143.  Hoiv  to  cause  a  plant  to  form  dew  at  any 
time.  —  By  putting  a  plant  in  the  same  conditions  as 


STEMS  107 

the  grass  at  night,  it  can  be  induced  to  form  dew. 
To  do  this,  set  a  large  glass  dish  over  a  vigorous  plant 
of  geranium  or  begonia  in  such  manner  that  it  will 
be  tightly  enclosed.  If  it  remains  in  this  position 
for  a  few  hours,  the  air  inside  the  vessel  becomes 
saturated  with  watery  vapor,  and  the  leaves  are 
unable  to  throw  off  any  more.  The  continued  sup- 
ply from  the  roots  is  forced  out  through  the  leaf  at 
the  edges  in  the  form  of  large  drops.  These  become 
so  large  that  they  fall  off  and  others  collect  in  the 
same  place,  so  that  moist  spots  will  be  formed  in  the 
soil  where  they  fall.  This  demonstration  will  be 
most  successful  if  the  plant  is  allowed  to  remain 
covered  over  night. 

144.  Lifting  poiver  of  leaves  and  tranches.  —  It 
has  been  shown  in  a  previous  experiment  (§  135) 
that  a  leafy  stem  will  pull  colored  fluid  upward 
in  the  stem,  and  if  proper  apparatus  were  at  hand 
it  could  be  proved  that  it  does  so  with  great  force. 
Both  the  lifting  power  of  the  leaves,  and  the  pump- 
ing power  of  the  roots  seem  insufficient  to  send  up 
the  necessary  amount  of  water  to  the  leaves,  for  it 
will  be  remembered  that  a  poplar  tree  uses  a  bar- 
rel or  more  of  water  every  day  during  the  summer, 


108  THE  NATURE  AND    WORK  OF  PLANTS 

and  smaller  quantities  at  other  times.  There  is 
still  much  to  be  found  out  about  the  ascent  of 
sap. 

145.  Growth  of  stems. — The  manner  in  which 
stems  grow  and  increase  in  size  bears  a  close  rela- 
tion to  the  arrangement  of  the  mechanical  elements. 
The  arrangement  of  the  living  tissues  is  different 
in  the  various  types,  of  course.  From  the  many 
forms  of  the  stem  it  will  be  most  profitable  to  select 
a  tree  and  the  cornstalk  for  study  of  this  feature. 

146.  Action  of  einhnjonk  tissue  of  a  tree.  —  The 
living  cells  of  a  tree  which  constantly  divide,  form- 
ing others  which  pass  into  dead  tissue,  lie  immedi- 
ately underneath  the  bark  and  completely  sheathe 
the  trunk,  forming  a  small  cone  of  delicate  cells  at 
the  tips  of  the  stems  and  branches  and  in  the  buds. 
Dead  cells  are  constantly  being  formed  on  the  inner 
side  of  this  layer  and  added  to  the  wood.  The 
cells  formed  in  any  one  season  are  distinguishable 
from  those  of  the  last  season  and  constitute  an 
annual  ring,  though  sometimes  two  rings  may  be 
formed  in  one  summer.  At  the  same  time  dead 
cells  are  being  added  to  the  bark  on  the  outer 
side   of   the   living   tissue.     The  living-  cells  at  the 


STEMS  109 

tip    divide    and   push   forward,   leaving    dead    cells 
behind  them. 

147.  Growth  in  length  and  diameter.  —  Dead  cells 
do  not  increase  in  size,  of  course,  so  that  the  trunk 
of  a  tree  does  not  elongate  except  at  the  tips  of 
the  stems  and  branches.  Thus  a  branch  on  the 
trunk  will  always  remain  the  same  distance  from 
the  roots.  Its  distance  from  the  ground  might  be 
increased  by  the  washing  away  of  the  soil  below  it. 
This  may  be  demonstrated  if  a  nail  is  driven  in 
the  trunk  of  a  tree  near  the  surface  of  the  soil, 
and  a  second  as  high  above  it  as  may  be  conven- 
ient. Measure  the  distance  between  them  quite 
exactly,  and  then  repeat  a  few  months  or  a  year 
later. 

148.  Measurement  of  growth  in  length.  —  Mark 
the  stem  of  some  rapidly  growing  plant,  such  as 
bean  or  sunflower,  with  India-ink  at  intervals  of 
half  an  inch.  Measure  these  intervals  on  three  or 
more  successive  days.  Do  all  of  them  increase  ? 
What  part  of  the  stem  increases  in  length  with 
greatest  rapidity? 

149.  Measurement  of  groivth  in  diameter.  —  The 
increase   in   diameter   of   a   plant   is   not   so   easily 


110  THE  NATURE  AND    WORK  OF  PLANTS 

obtained.  Perhaps  the  best  method  is  to  drive  two 
nails  into  the  opposite  sides  of  the  trunk  of  a  vigor- 
ous young  poplar  in  early  spring,  and  then  find 
the  exact  circumference  of  the  tree  an  inch  above 
these  nails  with  a  tape  measure.  Repeat  the  opera- 
tion of  measurement  about  the  first  of  September. 

150.  The  hark.  —  The  behavior  of  bark  should 
be  studied  in  connection  with  growth  in  thick- 
ness. The  yoimg  poplar  and  many  other  young 
trees  are  seen  to  have  a  smooth  bark,  while  older 
specimens  have  a  very  rough  or  even  a  shaggy 
covering.  The  cells  which  compose  the  bark  of  the 
younger  trees  are  alive,  and  divide  and  grow  in  such 
manner  that  they  keep  pace  with  the  increase  of 
the  trunk.  After  the  tree  reaches  a  certain  age 
the  bark  does  this  no  longer.  Any  increase  in  the 
trunk  then  results  in  the  splitting  of  the  bark, 
leaving  the  edges  exposed.  A  new  layer  of  bark 
is  formed  which  is  applied  to  the  inside  of  this  slit 
like  a  patch.  This  process  is  repeated  every  year, 
an,d  as  a  consequence  some  trees,  such  as  the  oaks, 
hickories,  and  poplars,  have  a  very  rough  or  shaggy 
bark.  The  sycamore  is  an  example  of  a  tree  which 
casts  away  the  old   layer   of   bark   each   year   and 


STE3f8  111 

presents  a  new  coat  of  smooth,  clean,  greenish 
white  bark  to  the  weather.  The  bark  serves  to 
protect  the  layer  of  living  tissue  from  damage  by 
the  climate,  or  by  animals,  or  from  the  falling 
trunks  or  branches  of  other  trees.  On  the  other 
hand,  the  numerous  crevices  afford  lodgment  and 
refuge  for  the  spores  of  parasitic  fungi  which  ger- 
minate and  injure  the  tree,  and  also  harbors  insects 
and  other  animals  which  work  injury  in  many 
ways. 

151.  Groivth  of  a  corn  stem.  —  Select  a  young 
and  rapidly  growing  corn  stem  and  mark  off  three 
or  four  of  the  terminal  internodes  into  half-inch 
intervals  by  means  of  India-ink.  Measure  these 
from  day  to  day  for  a  week.  What  places  show 
elongation  ? 

Trees  are  generally  larger  at  the  bases,  but  in  the 
corn  plant  and  in  the  palms  and  their  relatives  the 
basal  part  of  the  stem  will  be  found  to  be  smaller 
than  parts  of  the  stem  above  it.  This  is  due  to 
the  fact  that  such  stems  soon  reach  their  full  growth 
in  thickness  at  the  base,  and  the  later  portions 
formed  may  receive  more  food  and  attain  a  greater 
thickness. 


112  THE  NATURE  AND    WORK  OF  PLANTS 

152.  Noddiyig  or  circular  movements  due  to  un- 
equal growth.  —  Select  a  vigorous  specimen  of  the 
hop,  bean,  or  morning-glory,  and  tie  all  of  it  to  an 
upright  stake  except  the  tip  of  the  stem  a  foot  in 
length.  Now  set  a  second  thin  stake  in  the  ground 
so  that  its  top  is  just  below  the  tip  of  the  stem. 
Note  the  position  of  the  tip  an  hour  later.  If  it  has 
moved,  set  up  another  stake.  Repeat  this  process 
until  the  tip  has  moved  around  in  a  complete  circle. 
What  was  the  direction  of  the  movement?  What 
length  of  time  was  necessary  to  complete  the  circle  ? 
This  circular  movement  of  the  tip  is  due  to  the 
fact  that  one  side  of  the  stem  grows  faster  than 
the  other  sides  for  a  short  time,  then  it  slows  down 
and  a  region  next  to  it  grows  most  rapidly,  and 
so  on  around  the  stem.  This  results  in  tilting 
the  tip  toward  every  point  of  the  compass  in  suc- 
cession. 

A  nodding  movement,  due  to  the  alternate  growth 
of  two  sides  of  a  flattened  organ,  may  be  seen  if  the 
growing  leaves  of  narcissus  are  observed  in  this 
manner. 

153.  Length  of  life.  —  The  length  of  time  a 
single  specimen   of   a  plant  may  live    varies  enor- 


STEMS  113 

monsly.  Thus  in  some  of  the  lower  forms  an  indi- 
vidual may  be  grown  from  a  spore,  attain  maturity, 
give  rise  to  new  individuals,  and  die  in  a  few  hours 
or  even  in  a  few  minutes.  The  spores  of  these  same 
species  may  be  capable  of  living  many  years  in  a 
resting  condition,  however.  Among  the  seed  plants 
the  cycle  of  life  varies  from  sixty  or  seventy  days  in 
some  of  the  herbs  to  three  thousand  years  in  certain 
kinds  of  trees.  It  is  estimated  that  some  trees  can 
live  to  twice  this  age,  though  the  lack  of  records 
does  not  allow  this  to  be  verified.  The  estimation  of 
the  age  of  a  tree  by  counting  the  annual  rings  is 
subject  to  error,  since  the  number  of  these  rings  may 
be  nearly  twice  the  age  of  the  tree  in  years.  All 
seed  plants  may  be  roughly  classed  as  annuals,  bien- 
nials, and  perennials. 

154.  Annuals. — Annuals  are  those  which  live 
but  one  season.  The  seeds  germinate,  and  a  system 
of  roots,  a  stem,  and  branches  are  formed,  and  seeds 
are  matured  in  a  period  which  varies  from  two  to 
four  months.  Species  of  this  character  may  gener- 
ally be  distinguished  by  the  character  of  the  stem 
and  root  system.  Annuals  live  through  the  winter 
in  the  form  of  seeds  only.     Examine  twenty  species 


114  THE  NATURE  AND    WORK  OF  PLANTS 

and  select  the  annuals.     What  cultivated  plants  are 
grown  as  annuals? 

155.  Biennials.  —  A  second  group  of  species 
germinate  the  seeds,  form  a  stem  with  a  rosette  of 
leaves  and  an  extensive  root  system  in  one  year,  and 
then  develop  the  flower-bearing  branches,  flowers, 
and  seeds  the  second  season.  Some  of  the  thistles 
and  the  common  mullein  belong  to  this  class. 

156.  Perennials.  —  Quite  a  large  number  of  spe- 
cies germinate  the  seeds  and  form  stems  the  first 
year,  then  rest  during  the  winter,  and  continue 
growth  during  the  next  season  and  for  many  succes- 
sive seasons.  In  trees  and  similar  forms  the  entire 
stem  remains  alive,  and  consequently  it  increases  in 
bulk  each  year,  attaining  an  enormous  size.  The 
giant  trees  of  California  have  attained  a  trunk  about 
four  hundred  and  fifty  feet  high,  and  thirty  feet  in 
diameter.  These  are  by  no  means  the  tallest  trees 
in  the  world. 

Another  class  of  perennials  have  a  stem  which  lies 
just  underneath  the  surface  of  the  soil,  sending 
branches  up  into  the  air  each  year.  These  die  down 
on  the  approach  of  winter.  Meanwhile  the  under- 
ground stem  grows  at  the  tip,  and  would  increase  its 


STEMS  115 

length,  but  the  other  end  of  the  stem,  which  is  also 
the  oldest,  constantly  dies  away  so  that  the  plant 
does  not  greatly  increase  in  size.  The  great  size  of 
the  bulky  perennials  subjects  them  to  many  dangers 
which  the  underground  stem  does  not  incur,  and 
it  would  be  difficult  to  set  a  limit  to  the  age  which 
the  latter  may  reach.  The  ravages  of  animals,  ex- 
tremes of  heat  and  cold,  washing  away  of  the  soil  by 
rains,  or  the  growth  of  more  vigorous  species  around 
them,  would  tend  to  set  a  limit  to  the  age  which  they 
may  attain. 

157.  Changes  in  the  length  of  life  of  a  species.  — 
The  length  of  life  of  any  species  is  an  adaptation 
to  the  conditions  under  which  it  lives.  Changes 
may  be  brought  about  when  the  plant  is  introduced 
into  a  new  habitat.  Thus  the  ordinary  tomato  is 
an  annual,  as  it  is  grown  in  gardens ;  yet  if  it  is 
cultivated  in  a  greenhouse  and  sheltered  from  the 
weather,  it  may  live  two  or  three  times  as  long. 
Bringing  a  species  into  a  severer  climate  may  have 
the  effect  of  reducing  a  perennial  or  a  biennial  to 
an  annual. 

158.  Buds.  —  Immediately  underneath  the  epider- 
mis, or  bark,  lies  the  layer  of  living  tissue  which  is 


116  THE  NATURE  AND   WORK  OF  PLANTS 

capable  of  great  multiplication  of  cells  and  growth. 
At  certain  points  this  tissue  has  acquired  the  power 
of  forming  new  branches,  flowers,  and  leaves,  hence 
it  is  called  embryonic  tissue.  These  specialized 
masses  of  cells  are  generally  in  the  form  of  minute 
outgrowths,  and  are  located  at  the  tips  of  the  stem 
and  its  branches  as  well  as  in  the  axils  of  the 
leaves.  This  tissue  is  most  delicate  and  easily  in- 
jured, and  is  generally  protected  by  coverings  of 
leaves  or  bracts.  The  growing  points  or  masses  of 
embryonic  cells  and  their  coverings  form  buds. 

159.  Naked  hiids. — In  sJDecies  growing  in  tropi- 
cal and  mild  climates  the  buds  are  only  slightly 
shielded  by  the  young  leaves  near  the  tip  of  the 
stem,  and  no  special  coverings  are  developed.  Such 
an  arrangement  is  called  a  naked  hud,  and  an  ex- 
ample may  be  seen  m  the  cultivated  geranium  or 
pelargonium. 

160.  Scaly  huds.  —  Plants  which  grow  in  cold 
or  dry  climates  generally  adopt  some  method  of 
protecting  the  growing  points  from  damage.  The 
most  common  device  is  a  number  of  wrappings  of 
brownish  scales,  which  are  in  reality  a  special  form 
of   leaves  which  are  used  for  protection  instead  of 


STEMS  117 

food  formation.  The  scales  are  fitted  around  the 
growing  point  so  closely  as  to  make  a  compact 
conical  mass  that  is  very  firm.  In  addition  the 
scales  are  often  furnished  with  a  coat  of  hairs  or 
a  layer  of  balsam  or  varnish  which  makes  them 
absolutely  waterproof.  These  scales  do  not  keep 
the  growing  plant  warmer  than  the  surrounding 
air,  but  they  protect  it  from  damage  by  ice  or  frost, 
and  also  prevent  drying  out. 

161.  Buds  of  the  apple.  —  Secure  some  winter 
buds  of  the  apple  by  cutting  off  twigs  two  feet  in 
length  two  weeks  before  the  subject  is  to  be  studied, 
and  placing  the  cut  ends  of  the  stems  in  a  dish  of 
water  in  a  warm  room.  Now  carefully  dissect  some 
buds  freshly  procured  from  the  tree.  Take  off 
the  scales,  one  at  a  time,  noting  the  manner  in 
which  they  are  fitted  to  each  other.  The  central 
mass  of  the  bud  should  contain  the  young  leaves 
and  perhaps  flowers.  Tear  apart  and  note  shape 
and  size.  Later  examine  the  opening  buds.  What 
changes  have  taken  place  which  would  cause  the 
scales  to  come  apart?  and  what  changes  have 
occurred  in  the  shape  and  size  of  the  leaves  and 
flowers?     Note  all  these  points  by  sketches. 


118  THE  NATURE  AND    WORK  OF  PLANTS 

162.  Buds  of  elder,  maple,  or  elm.  —  Sketch  a 
twig  of  one  of  these  plants,  showing  the  leaf  scars 
and  the  position  and  size  of  the  buds.  Treat  as 
above. 

163.  Sleejmig  huds.  —  It  is  to  be  seen  that  a 
bud  is  simply  a  young  branch,  and,  furthermore, 
that  all  the  branches  of  the  plant  are  developed  in 
this  manner.  It  is  important,  therefore,  that  the 
plant  should  be  furnished  with  an  ample  supply  of 
them,  so  that  the  destruction  of  a  few  need  not 
deprive  it  entirely  of  the  power  of  making  new 
branches.  There  is  one  or  perhaps  more  of  these 
growing  points  at  the  base  of  every  leaf.  Only  a 
small  proportion  of  them  develop  in  any  year,  the 
remainder  lying  quiescent,  and  may  continue  to  do 
so  for  years,  being  known  as  sleejnng  huds.  Many 
of  these  structures  may  be  found  on  the  lower 
parts  of  the  stems  of  young  trees. 

164.  The  aioakening  of  sleejmig  huds.  —  If  the 
top  of  a  tree  is  cut  off,  some  of  the  sleeping 
buds  remaining  on  the  upper  part  of  the  stem 
start  into  life,  developing  branches,  and  giving  the 
plant  a  low,  compact   appearance.     In  the  pruning 


STEMS  119 

of   fruit  trees   the   sleeping  buds   are   often   called 
into  action. 

165.  Winter  huds  of  aquatic  ^9/a?i^s.  —  In  one 
class  of  land  plants  the  upper  branches  of  the  stem 
have  been  seen  to  die  down,  leaving  only  the  basal 
portion  of  the  stem  with  its  buds  to  live  through  the 
winter.  Exactly  the  reverse  action  takes  place  in 
some  aquatic  plants  which  root  in  the  bottom  of 
streams  or  lakes,  or  which  float  on  the  surface.  If 
a  visit  is  made  to  a  lake  or  pond  about  the  time  that 
the  trees  have  lost  all  their  leaves,  this  curious  bud 
formation  may  be  found.  The  stems  of  the  pond- 
weeds,  stonewort,  bladderwort,  and  others  will  be 
seen  to  have  taken  on  a  brownish  color  except  at 
the  tips.  Here  the  stem  is  still  alive,  and  a  large 
number  of  leaves  of  a  dark  green  color  overlap  each 
other  closely,  forming  an  egg-shaped  mucilaginous 
mass.  Break  off  some  of  these  buds  and  find  if 
they  will  float  alone.  These  buds  are  sometimes 
termed  hibernacula.  Preserve  your  notes  upon  the 
subject  and  visit  the  same  pond  in  the  following 
spring  as  soon  as  the  ice  has  melted.  A  great  num- 
ber of  the  winter  buds  may  be  seen  floating  near 
the  surface  of  the  water.     Examine,  and  note  their 


120  TUE  NATURE  AND    WORK  OF  PLANTS 

identity  with  the  kinds  seen  the  previous  autumn. 
They  are  plentifully  furnished  with  red  and  purple 
coloring  matter  as  a  result  of  the  low  temperatures 
under  which  they  have  lived. 

166.  Behavior  of  the  hibernacula. — The  hiber- 
nacula  sink  to  the  bottom  of  the  water  in  the 
autumn,  and  thus  escape  the  action  of  the  ice.  This 
is  also  done  by  the  minute  pond-scums  and  other 
forms  which  are  seen  to  float  on  the  surface  in  great 
quantity  in  the  summer.  When  the  ice  disappears 
in  the  spring  and  the  sun's  rays  begin  to  warm  the 
water,  several  bubbles  of  gas  are  formed  in  them, 
which  helps  float  them  to  the  surface.  Now  the 
bud  begins  to  unfold,  and  the  tip  of  the  enclosed 
stem  to  grow  in  length,  while  long  roots  grow  out 
from  the  basal  end.  Perhaps  it  finds  lodgment  in 
the  mud  in  shallow  water,  and  the  new  season's  work 
is  begun. 

All  water  plants  do  not  form  such  buds.  Water 
lilies  have  great  stems  lying  imbedded  in  the  mud  at 
the  bottom  of  the  pond,  and  these  send  up  leaf  and 
flower  stalks  which  reach  the  surface  and  perform 
their  function  during  the  summer,  dying  down  on 
the  approach  of  cold  weather. 


STEMS  121 

167.  Bulhs.  —  Split  an  onion,  hyacintli  bulb,  or 
any  similar  structure.  It  will  be  seen  tliat  it  is 
simply  a  great  bud,  with  the  scales  which  surround 
the  growing  point  very  much  thickened  and  loaded 
with  food.  The  centre  of  the  bud  is  a  short,  thick- 
ened stem.  Bulhs  are  buds  that  are  usually  detached 
from  the  plant  as  soon  as  they  are  formed,  and  when 
they  grow,  they  as  well  as  hibernacula  make  a  new 
individual  and  therefore  serve  to  reproduce  the 
species  (§  183). 

168.  Corms.  —  An  interesting  method  by  which 
delicate  plants  endure  a  severe  winter  consists  in  the 
formation  of  short,  thick,  upright  stems,  like  those 
of  the  calla  or  the  jack-in-the-pulpit.  Examples  of 
the  latter  may  be  found  in  almost  any  woods.  On 
the  upper  side  of  such  short  squat  stems  may  be 
found  a  large  conical  bud,  covered  by  a  few  large 
scales,  wrapped  tightly  around  the  central  mass. 
Cut  open  such  a  bud;  the  young  leaves  and  flowers 
for  the  next  season  will  be  found  perfectly  formed, 
except  in  size,  as  early  as  June  or  July,  ten  months 
before  they  are  to  be  called  into  action. 

169.  Forcing,  or  inducing  an  earlier  growth. — If 
these  corms  are  taken  from  the  soil  in  the  autumn 


122  TUE  NATURE  AND    WOEK  OF  PLANTS 

and  allowed  to  remain  out  of  doors  in  the  cold  until 
the  first  of  December,  then  put  in  a  cellar  for  a 
month  or  two,  they  may  then  be  potted  and  will 
begin  to  grow.  Note  the  behavior  of  the  bud  cover- 
ing. It  does  not  burst  open  immediately,  but  elon- 
gates until  it  reaches  the  surface  of  the  soil,  and  then 
only  does  it  open  and  expose  the  young  leaves.  Set 
the  pot  with  the  growing  bud  in  a  dark  room,  or 
cover  it  with  a  pile  of  moss.  The  bud  will  con- 
tinue to  elongate  until  it  reaches  the  light,  or  it  has 
attained  a  length  of  seven  or  eight  inches,  which 
seems  to  be  its  limit  of  growth.  Its  purpose  is  to 
bring  the  leaves  above  the  surface  of  the  ground,  and 
it  does  not  open  until  it  is  struck  by  the  light,  which 
is  usually  a  signal  that  this  has  been  accomplished. 

170.  So7ne  protective  devices  of  the  shoot. — 
Leaves  and  stems  are  subject  to  destruction  by 
animals  which  use  them  for  food,  and  a  large 
number  of  species  are  furnished  with  structures 
which  hinder  or  prevent  attack  by  the  animal.  The 
most  common  means  of  protection  consists  in  poison- 
ous or  hitter  substances  in  the  tissues,  spines,  prickles, 
hristles,  thorns,  and  stinging  hairs. 

The  acrid  burning  sensation  which  follows  tasting 


STEMS  123 

jcack-in-the-pulpit  preserves  it  from  the  ravages  of 
grazing  animals,  and  the  well-known  qualities  of  the 
poison  ivies  serve  a  similar  purpose.  The  active 
substance  in  the  latter  case  is  an  oil  secreted  by  the 
leaves  and  stems,  making  even  proximity  dangerous 
to  the  animal. 

The  prickles  of  roses  and  other  shrubs  are  exam- 
ples of  Aveapons  coming  from  the  epidermis  of  the 
stems,  and  which  may  come  away  in  the  body  of 
the  animal  which  comes  into  contact  with  the  stems. 
The  thorns  of  many  species,  including  the  well- 
known  honey  locust  (Gleditschia),  are  branches  which 
have  altered  their  method  of  growth  in  such  manner 
that  they  are  very  effective  weapons  for  defence. 

The  edges  of  the  leaves  of  some  grasses  are  cut 
into  saw  teeth,  and  these  are  edged  with  silica  so 
finely  that  they  cut  the  flesh  like  knives.  The  mar- 
gins and  surfaces  of  thistle  leaves  and  stems  are 
drawn  out  into  spines,  the  protective  value  of  which 
may  be  easily  seen. 

The  members  of  the  cactus  family  protect  their 
bodies  to  a  great  extent  by  sharp  spines,  many  of 
which  are  harhed.  These  spines  are  modified  leaves 
which  have  lost  the  original  function  of  such  organs, 
and  have  become  solely  organs  of  defence. 


124  THE  NATURE  AND    WORK  OF  PLANTS 

Animals,  on  the  other  hand,  are  constantly  strivmg 
to  use  the  bodies  of  these  plants  for  food  without 
injury  from  their  weapons,  and  some  of  them  suc- 
ceed even  with  such  well-protected  forms  as  the 
cactus  and  the  thistle.  Some  grazing  animals  may 
even  eat  poison  ivy  without  harm. 

171.  Branches  used  as  leaves.  —  A  species  may 
find  itself  in  a  location  to  which  its  leaves  are  wholly 
unsuited,  and  it  may  cease  to  develop  these  organs 
in  the  usual  way.  In  such  instances  branches  are 
sometimes  modified  to  carry  on  the  work  that  should 
be  done  by  the  leaf.  An  example  of  this  may  be 
seen  in  the  "smilax  "  of  the  gardener,  which  is  used 
so  profusely  for  decorative  purposes.  The  slender, 
thin  bodies  having  the  appearance  of  leaves  are 
really  short  branches,  and  the  true  leaves  are  to  be 
found  as  small  colorless  or  brownish  bracts  at  the 
lower  side  of  the  base  of  these  leaflike  branches. 

172.  Tlie  jpart  of  stems  in  the  struggle  for  exist- 
ence. —  If  the  surface  of  the  earth  were  level  and 
plain,  and  the  number  of  plants  were  not  so  great 
as  to  fully  occupy  this  space,  probably  all  species 
would  form  short  stems  which  would  simply  lift  the 
leaves  and  flowers  fi'om  the  ground. 


STEMS  125 

The  number  of  individuals  which  attempt  to  grow 
on  any  given  spot,  however,  is  many  times  greater 
than  it  can  support.  The  species  which  are  capable 
of  sending  up  long  stems  quickly  will  reach  the 
sunlight  and  live  while  their  slower  and  weaker 
neighbors  will  be  choked  or  shaded  out.  In  this 
fight  the  stem  is  the  chief  weapon. 

173.  Weeds. — In  the  cultivation  of  crop  plants 
all  species  are  killed  by  the  farmer  except  the  one 
desired,  thus  removing  it  from  the  struggle  for 
existence  with  neighbors.  Certain  forms,  however, 
have  habits  of  growth  which  adapt  them  for  gaining 
a  foothold  among  the  cultivated  forms,  and  this 
makes  them  weeds.  Before  the  country  was  settled 
or  cultivated  there  were  no  weeds,  of  course.  Vigor- 
ous and  rapid  growth  of  the  stems  is  the  principal 
characteristic  of  weeds.  The  stems  do  not  alwaj^s 
stand  erect,  but  may  carpet  the  soil  and  hinder  the 
growth  of  other  plants  in  this  manner.  Find  and 
describe  the  habits  of  three  weeds. 

174.  Climbing  stems.  —  In  the  struggle  to  get 
the  leaves  and  flowers  up  to  the  sunlight,  a  number 
of  species  have  formed  the  habit  of  clinging  to  the 
stems  of  other  plants.    This  is  done  by  two  methods : 


126  THE  NATURE  AND    WORK  OF  PLANTS 

the  stem  of  the  climber  may  coil  or  twine  around  the 
body  of  the  supporting  plant,  or  it  may  attach  itself 
by  means  of  roots  or  tendrils. 

The  hop  and  morning-glory  are  examples  of  the 
twiners,  and  the  circular  movement  of  the  tips  of  the 
stems  is  one  of  the  factors  in  coiling  it  round  the  sup- 
port. Examine  one  of  these  plants,  or  a  bean  vine, 
and  note  the  firmness  with  which  it  is  attached. 

That  plants  climb  by  means  of  roots  has  already 
been  noticed  (§  28).  The  most  effective  climbing 
devices,  however,  are  tendrils.  These  are  generally 
modified  stems,  branches,  flower  stalks,  or  even 
leaves. 

Examine  the  tendrils  of  a  squash,  pumpkin,  pas- 
sion flow^er,  or  balsam  apple  (MicramjMlis).  They 
will  be  seen  to  be  long  slender  bodies  arising  at  the 
nodes  of  the  stem  at  the  bases  of  the  leaves.  Ob- 
serve their  movement  in  the  same  manner  as  in  the 
stems  (§152).  The  tendril  appears  to  be  curved,  with 
a  hooked  tip.  Draw  its  exact  outline.  Now  rub  the 
surface  on  the  inner  side  of  the  curve  with  a  pencil, 
and  look  for  changes  in  form.  It  curves  at  the  place 
touched.  Take  note  of  the  time  and  extent  of  the 
movement.  If  the  pencil  were  held  in  place,  the  ten- 
dril would  coil  around   it.      Look  for  instances   of 


STEMS  127 

tendrils  which  have  just  formed  a  coil  around  a  sup- 
port. Now  observe  the  older  tendrils  toward  the 
base  of  the  stem.  What  other  action  has  the  ten- 
dril shown  beside  coiling  around  the  support  ?  The 
formation  of  the  spiral  coils  shortens  the  tendril  and 
brings  the  stem  nearer  the  support.  Thus  as  the  tip 
of  the  stem  elongates  these  organs  are  formed  at 
each  node,  and  they  revolve  in  the  air  until  coming 
in  contact  with  a  support:  quickly  coiling  round 
this,  the  free  portion  of  the  organ  is  thrown  into  a 
coil  lifting  up  the  stem  a  distance  of  a  few  inches. 
The  force  exerted  in  the  lifting  would  raise  a  weight 
of  one  to  three  ounces,  which  is  much  more  than  the 
weight  of  the  stem  to  which  the  tendril  is  attached. 
Compare  the  action  of  the  tendrils  of  three  species. 
After  the  body  of  the  plant  has  been  fastened  to  the 
support  by  means  of  the  tendrils,  the  coiled  portions 
act  as  springs  in  resisting  the  action  of  the  wind  or 
any  other  force  which  would  tend  to  tear  the  plant 
from  its  support.     Test  this  by  hand. 

175.  77ie  irritability  or  sensitiveness  of  stems.  —  It 
has  been  shown  in  a  previous  paragraph  (§91)  that 
the  light  which  shines  on  the  leaf  may  send  an  im- 
pulse to  the  stem  to  which  it  is  attached,  causing  a 


128  THE  NATURE  AND    WORK  OF  PLANTS 

curvature  which  will  place  the  leaf  in  the  most 
advantageous  position  for  the  performance  of  its 
work.  The  stem  is  sensitive  to  light  itself,  as  may 
be  shown  if  a  specimen  stripped  of  leaves  is  placed 
near  a  window,  when  it  can  be  seen  to  bend  toward 
the  light. 

176.  Sensitiveness  to  gravity. — Select  a  vigor- 
ously growing  specimen  of  a  tomato  planted  in  a 
pot,  and  place  it  with  the  stem  in  a  horizontal  posi- 
tion. Observe  the  stem  a  day  later.  In  what 
region  has  the  curvature  taken  place  ?  Repeat  this 
experiment  with  a  grass.  Note  the  stems  of  plants 
in  the  woods  and  meadows  which  have  been  thrown 
down  by  the  wind  or  other  causes,  and  the  tips  have 
curved  in  response  to  gravity.  This  form  of  geotro- 
pism  is  exactly  the  reverse  of  that  exhibited  by  roots. 
(See  §  43.)  Still  another  response  to  gravity  is  to  be 
seen  in  the  lateral  branches  of  coniferous  trees  and 
trailing  stems.  These  place  their  axes  at  right 
angles  to  the  action  of  gravity.  Sometimes  the 
trailing  habit  is  the  result  of  the  action  of  the  plant 
in  placing  its  axis  at  right  angles  to  the  rays  of  light 
which  strike  it.  If  the  plant  is  placed  in  darkness, 
it  may  be  found  whether  the  horizontal  position  is 


STEMS  129 

the  result  of  the  action  of  gravity  or  light.  If  it  is 
the  result  of  light,  it  will  generally  grow  erect  in 
darkness. 

177.  Stems  are  found  among  the  higher  plants 
only.  —  The  seed  plants  and  ferns  only  have  true 
stems  as  determined  by  the  tissues  which  compose 
them.  The  mosses,  liverworts,  and  some  of  the  sea- 
weeds have  a  main  axis  from  which  branches  are  sent 
off,  and  while  it  performs  the  work  of  a  stem  it  has 
not  the  true  stem  structures.  A  body  of  this  kind 
is  termed  a  thallus.  The  main  axis  of  the  mosses, 
liverworts,  and  the  larger  algae  is  often  designated 
as  a  stem,  though  it  does  not  exhibit  the  distinction 
of  tissues  shown  by  the  true  stems  of  the  higher 
plants. 


VII.     THE   WAY    IN   WHICH    NEW    PLANTS 
ARISE 

178.  Distribution  of  the  individuals  of  a  species. 
—  Every  species  is  represented  by  a  number  of 
individuals.  Sometimes  this  number  is  very  great 
and  may  run  up  into  the  millions.  On  the  other 
hand,  there  are  a  number  of  species  of  which  but 
few  individuals  have  been  seen,  and  some  are  so 
rare  that  but  a  single  specimen  may  have  been 
found.  The  individuals  of  a  species  may  be  scat- 
tered across  states  and  continents,  or  they  may  be 
congregated  in  a  meadow  or  on  a  single  mountain 
top.  Thus,  for  instance,  the  common  polypody 
forms  carpets  or  dense  layers  on  rocks,  that  contain 
several  dozens  of  individuals,  and  these  colonies  may 
be  found  almost  throughout  North  America,  Asia, 
and  Europe.  The  individuals  of  Adam-and-Eve,  or 
putty  root,  occur  one  or  a  few  in  a  place,  in  a 
broad  belt  of  country  that  includes  the  northern 
half  of  the  United  States  and  the  southern  half 
of   Canada.     The  Georgia  oak  {Quercus  Georgiana) 

130 


THE   WAY  IN   WHICH  NEW  PLANTS  ARISE       131 

is  found  only  on  the  granite  slopes  of  Stone  Moun- 
tain in  Georgia. 

Every  species  originated  in  some  one  locality,  and 
it  spreads  its  seeds  or  spores  by  various  methods. 
The  spores  or  seeds  find  a  foothold  wherever  they 
may  in  suitable  places.  Probably  no  species  has 
succeeded  in  sending  seeds  or  spores  to  all  of  the 
places  which  would  be  suitable  for  its  growth.  As 
the  species  spreads  across  a  continent,  it  may  meet 
barriers  in  the  form  of  seas,  mountains,  or  other 
obstacles  which  stop  its  progress. 

179.  Methods  of  reproduction.  —  The  life  of  each 
individual  is  limited,  and  no  matter  whether  the 
number  is  great  or  small,  if  each  does  not  constantly 
give  rise  to  new  individuals  the  species  would  soon 
become  exterminated.  Furthermore  new  individuals 
must  be  produced  as  fast  as  the  older  ones  die,  or 
extermination  will  result.  Numerous  species  of  ani- 
mals have  disappeared  in  the  memory  of  man,  but 
modern  examples  of  the  extinction  of  plants  are  not 
common,  although  the  earth's  crust  is  rich  with  the 
remains  of  species  existent  in  former  geologic  periods. 
A  tree  belonging  to  the  sunflower  family,  once  found 
on  the  island  of  Saint  Helena,  is  known  to  be  ex- 


132  THE  NATURE  AND    WORK  OF  PLANTS 

tinct.  There  are  three  principal  methods  by  which 
new  individuals  may  be  formed :  vegetative  repro- 
duction by  means  of  cuttings,  huds,  branches,  etc., 
simple  or  asexual  spores,  and  egg  formation. 

180.  Hej^roduction  by  cuttings.  —  Select  a  good 
healthy  leaf  of  a  begonia,  cut  it  from  the  stem, 
trim  away  nearly  half  of  it,  and  put  the  raw  edge 
in  sand  kept  moist  in  a  shallow  dish  or  box.  Ex- 
amine every  week  for  a  month.  Roots  will  first  be 
formed,  and  then  if  the  experiment  is  allowed  to 
run  long  enough  a  stem  will  appear,  which  will  in 
turn  bear  leaves  like  the  original  from  which  the 
cutting  was  made.  It  is  seen  that  the  begonia  is 
able  to  replace  the  entire  plant  from  part  of  a  leaf 
—  a  capacity  that  is  shared  by  an  extremely  large 
number  of  species. 

181.  TJie  stem  may  rejjroduce  the  entire  plant.  — 
Cut  a  small  twig  of  the  willow,  a  stem  of  the  ge- 
ranium, coleus,  or  begonia,  and  insert  in  moist  sand 
as  above.  A  few  weeks  later  the  cutting  will  be 
found  to  have  replaced  the  missing  roots  and  leaves 
and  made  a  complete  plant. 

182.  Tlie  root  may  reproduce  the  plant.  —  Cut  off 
a  portion  of   the  fleshy  root  of  a  sweet   potato    or 


THE   WAY  IN    WHICH  NEW  PLANTS  ARISE       133 

horse  radish,  and  put  in  moist  sand  or  soil.  Stems 
and  leaves  will  be  seen  to  appear  after  a  time.  The 
ability  to  replace  the  other  members  of  the  plant 
by  the  root  is  not  very  common.  It  is  shared,  how- 
ever, by  beech,  cherry,  poplar,  and  some  coniferous 
trees. 

183.  Structures  used  hy  2^^ants  as  means  of  vege- 
^tative  reproduction.  —  Plants  have  many  devices  by 
which  portions  of  the  roots,  stems,  and  leaves  take 
on  special  forms  and  become  separated  from  the 
parent  plant  in  a  manner  which  allows  them  to  form 
a  new  individual.  Chief  among  these  structures  are 
bulbs  (see  §  167),  hidhils,  tubers,  offsets,  stolons,  besides 
many  special  forms. 

184.  Tubers. — -A  tuber  consists  of  a  portion  of 
an  underground  stem  which  serves  as  a  storehouse 
for  surplus  food,  and  which  is  capable  of  reproduc- 
ing the  plant  by  the  growth  of  its  buds,  which  are 
usually  several  in  number.  Examine  the  base  of  a 
vigorous  potato  stem  by  digging  away  the  soil.  Be- 
sides the  roots  will  be  found  numbers  of  thickened 
stems  or  potatoes.  Note  the  "  eyes,"  or  buds,  on 
the  surface.  Are  they  most  abundant  on  the  end 
toward  the  main  stem  or  the  apical  end  ? 


134  THE  NATURE  AND    WORK  OF  PLANTS 

The  main  stem  dies  at  the  close  of  the  season, 
leaving  the  tubers  in  the  soil,  and  if  each  were 
capable  of  giving  rise  to  one  plant  alone,  the  parent 
plant  would  be  followed  by  a  dozen  or  more  the 
next  season.  This  does  not  express  the  full  repro- 
ductive power  of  the  tubers,  however.  In  the  plant- 
ing of  "  seed"  potatoes  to  obtain  a  crop,  the  farmer 
cuts  the  tubers  into  pieces  each  of  which  contains  an 
"  eye  "  and  is  capable  of  giving  rise  to  a  new  plant. 
As  a  consequence  the  tubers  of  a  single  plant  may  be 
capable  of  producing  over  a  hundred  new  individuals. 

Secure  a  large,  sound  potato  in  January  and  put 
it  in  the  mouth  of  a  large  bottle  filled  with  water, 
or  a  cup  or  tumbler,  cover  with  a  glass  dish  and  set 
in  a  living  room.  Renew  the  water  and  clean  the 
bottle  occasionally.  Note  the  manner  in  which  the 
buds  begin  to  grow  and  their  location.  Do  all 
the  buds  awake  ?  If  several  experiments  have  been 
set  up,  you  can  awaken  the  sleeping  buds  by  destroy- 
ing the  active  ones.  Are  new  roots  formed  on  the 
tuber  or  on  the  stems?  Observe  the  behavior  of 
potatoes  which  have  sprouted  in  a  dark  cellar. 

185.  Bulbils  and  hulhlets.  —  It  has  been  shown 
how   the   underground   branch    enclosed   in    a   bud 


THE   WAY  IN    WHICH  NEW  PLANTS  ARISE       135 

may  increase  in  thickness,  and  develop  its  sheathing 
scales  in  such  manner  as  to  form  an  onion  or  other 
bulbs.  The  buds  in  the  upper  axils  of  a  shoot  may 
also  exhibit  this  same  action,  but  the  resultant 
structures  are  generally  smaller  and  are  termed 
hulhils  or  hulhlets  by  some  authors.  Thus  the  onion 
may  produce  the  last-named  formations  on  the 
upper  ends  of  its  stems.  In  this  instance  the  bulb- 
let  replaces  the  flower  bud.  This  behavior  may  be 
noted  in  the  cultivated  onion  as  well  as  in  the  wild 
garlic  {Allium  vineale  L.),  meadow  garlic  [Allium 
Canadense.L.),  sometimes  in  the  wild  onion  {Allium 
mutabile  Michx). 

The  conversion  of  a  leafy  bud  into  a  bulblet  is 
to  be  seen  in  the  tiger  lily,  in  which  small  blackish 
bulblets  covered  with  three  or  four  scales  are  to  be 
found  in  the  upper  axils.  These  may  germinate  as 
soon  as  they  fall  to  the  ground,  and  sometimes  send 
out  roots  before  they  are  detached  from  the  parent 
plant.  The  bulblets  of  the  lily  as  well  as  those  of 
the  dioscorea,  a  member  of  the  yam  family,  will 
endure  long  periods  of  drought  and  low  temperature 
without  injury. 

The  bulb-bearing  loosestrife,  found  in  marshes  and 
damp    thickets   in   Northern   United   States,   forms 


136  THE  NATURE  AND    WOBK  OF  PLANTS 

reddish  cigar-shaped  bulbils  in  the  upper  axils  of  the 
stems,  which  consist  of  a  thickened  branch  sheathed 
by  blunt  scales.  These  structures  drop  from  the 
plant  in  the  autumn,  and  those  which  fall  in  the 
water,  or  those  which  are  covered  up  by  falling 
leaves,  escape  frost  and  germinate  in  the  following 
spring,  reproducing  the  plant.  Those  that  drop  into 
the  water  may  be  carried  away  by  currents,  and 
thus  spread  the  species  into  unoccupied  territory. 

Cystopteris  (C.  hulbifera),  a  common  fern,  forms 
numerous  -bulblets  on  the  lower  surfaces  of  the  mid- 
ribs, which  drop  off  in  the  autumn  and  germinate  in 
the  spring. 

186.  Division  of  the  body  hy  the  death  of  j)cirt  of 
it.  —  Some  of  the  liverworts,  club-mosses,  ferns,  and 
many  of  the  seed  plants  have  creeping  underground 
stems  which  branch  in  the  form  of  a  letter  Y.  By 
the  death  of  the  older  part  of  the  stem,  representing 
the  base  of  the  Y,  the  two  branches  are  left  as 
separate  plants.  These  extend,  branch,  and  divide  in 
the  same  manner.  Note  this  process  in  the  com- 
mon liverwort  (Marchantia,  or  Conocephalus),  in  the 
rhizomes  of  the  fern  and  club-moss.  It  may  be  seen 
also  in  the  creeping  grasses. 


THE   WAY  IN    WHICH  NEW  PLANTS  ARISE      137 

187.  Division  among  the  simjjle  ^;?a?i^s.  —  Among 
the  forms  in  which  the  body  consists  of  a  single  cell 
new  ones  are  formed  by  the  division  of  a  parent  cell, 
and  the  two  halves  quickly  grow  to  the  size  of  the 
original  cell,  when  they  divide  in  turn.  Such  organ- 
isms grow  with  great  rapidity,  and  this  method  gives 
rise  to  a  large  number  of  individuals  in  a  very  short 
time.  But  fifteen  or  twenty  minutes  are  necessary 
to  enable  each  cell  to  attain  full  size  and  divide.  By 
this  method  a  single  cell  of  a  bacterium  may  produce 
sixteen  million  others  in  eight  hours,  and  in  a  day 
many  millions  of  millions. 

188.  Runners.  —  Many  species  of  seed  plants 
send  out  long  branches  with  slender  internodes  from 
the  bases  of  the  main  stalks,  and  these  lie  on  the 
surface  of  the  ground  forming  roots  at  each  joint  or 
node.  Leaves  are  also  formed,  and  later  an  upright 
stem.  Then  the  runner  itself  dies  away,  leaving  a 
young  plant  to  mark  the  position  of  each  node. 
This  process  may  be  followed  in  any  strawberry 
bed,  and  is  a  very  efficient  method  of  spreading  the 
plant. 

189.  Stolons.  —  The  dewberries  of  pastures,  some 
raspberries,   and   other   plants,   form   slender   stems 


138  THE  NATURE  AND    WORK  OF  PLANTS 

which  finally  lean  over  with  their  tips  touching 
the  ground.  Roots  are  formed  at  this  point,  and 
the  growth  of  leaves  and  a  new  main  stem  quickly 
follows,  making  a  new  individual. 

190.  Dissemination  or  sjoreading  of  the  2^^<^nt  hy 
vegetative  propagation.  —  In  all  of  the  above  methods 
by  which  new  individuals  are  formed  from  portions 
of  the  body  of  a  parent  plant,  the  new  specimen 
finds  a  foothold  a  greater  or  less  distance  from  the 
parent.  Each  successive  set  of  new  plants  is  still 
farther  away  from  the  starting  point,  and  it  is  to  be 
seen  that  any  species  might  travel  considerable  dis- 
tances by  such  seemingly  slow  methods.  Thus  some 
of  the  young  plants  formed  by  the  runners  of  a 
strawberry  will  be  five  feet  from  the  parent,  and  as 
these  quickly  give  rise  to  similar  runners  the  species 
would  travel  across  a  large  meadow  in  a  few  years. 

191.  Ge7nmce. — If  the  upper  surfaces  of  flat 
fronds  of  Marcliantia  ov'  Lunularia  are  examined, 
small  circular  or  crescent-shaped  receptacles  will  be 
seen  containing  a  number  of  globose  masses  of  green 
tissue  either  loose  or  easily  detached.  These  are 
the  portions  of  its  body  devised  to  reproduce  the 
species    vegetatively,   and    are   termed   gemmce.      If 


THE   WAY  IN    WHICH  NEW  PLANTS  ARISE      139 

placed  on  damp  soil  covered  with  a  dish  in  a  warm 
room,  they  may  be  seen  to  germinate. 

192.  Be2:)7'oduction  hy  sjjores.  —  Instead  of  cut- 
ting off  a  member  of  its  body  for  the  purpose  of 
giving  rise  to  new  individuals,  the  plant  may  develop 
special  masses  of  reproductive  tissue.  When  these 
masses  reach  maturity,  they  divide  into  a  number 
of  separate  cells,  each  of  which  is  capable  of  giving 
rise  to  a  new  individual  upon  germination r  The 
origin  of  new  individuals  in  this  manner  is  termed 
asexual  rej^roduction,  and  the  spores  in  a  puff  ball, 
or  those  on  the  under  side  of  a  fern  leaf,  exhibit 
this  action. 

193.  JReprodiiction  hy  eggs. — In  another  method 
of  reproduction  the  plant  develops  two  kinds  of 
reproductive  tissue,  and  when  these  are  mature  a 
cell  from  each  unite  to  form  a  fertilized  egg,  which 
then  is  capable  of  giving  rise  to  a  new  individual. 
The  two  kinds  of  reproductive  elements  are  termed 
gametes,  and  the  origin  of  new  plants  by  this  method 
constitutes  sexual  rejjroductio?!. 

194.  Fern  spores. — Examine  the  under  side  of 
the  leaves  or  fronds  of  the  polypody  or  any  com- 
mon fern  in  the  autumn.     A  number  of  brown  spots, 


140  THE  NATURE  AND    WORK  OF  PLANTS 

masses,  or  areas  will  be  seen.  After  they  are  com- 
pletely ripe,  strike  a  sheet  of  white  paper  with  the 
frond.  A  quantity  of  brownish  particles  will  be 
thrown  out  on  the  paper.  Examine  with  a  lens. 
They  appear  to  be  roughened  balls  or  egg-shaped 
masses.  These  are  the  asexual  spores  of  the  fern. 
Now  examine  the  masses  on  the  fern  leaf  with  the 
lens.  The  spores  have  been  enclosed  in  flasks  or 
capsules  with  short  stalks.  Sometimes  the  collec- 
tion of  capsules  is  covered  with  a  shield,  or  by  the 
upturned  edge  of  the  frond. 

Secure  a  small  piece  of  a  leaf  of  any  common 
fern  with  mature  spore  cases.  Allow  it  to  become 
quite  dry.  Now  lay  it  with  the  spore  surface 
upward  on  a  sheet  of  white  blotting  paper  satu- 
rated with  water,  and  cover  with  a  glass  dish. 
Remove  the  dish  and  examine  a  day  later.  Numer- 
ous brown  spores  will  be  seen  scattered  over  the 
blotting  paper  in  all  directions.  The  spores  are 
thrown  out  in  a  cloud  by  ferns  in  damp  weather 
by  the  action  of  the  capsules  in  which  they  are 
formed. 

A  great  many  of  the  mosses  and  liverworts  are 
known  also  to  reproduce  themselves  by  means  of 
various  kinds  of  bulbils,  cuttings,  and  similar  parts. 


TUE   WAT  IN   WHICH  NEW  PLANTS  ARISE      141 

and  this  in  many  cases  is  the  only  way  which  they 
have  of  perpetuating  the  species. 

195.  Germination  of  spores.  —  Take  a  small  piece 
of  soft  brick,  and  boil  it  thoroughly  to  kill  all 
organisms  attached  to  it.  After  it  has  been  in 
the  water  for  an  hour,  remove  and  set  in  a  saucer 
of  spring  water.  Cover  with  a  tumbler.  After  it 
is  cool  sprinkle  spores  from  some  fern  liberally  over 
its  surface.  Replace  the  cover.  Heplenish  the  water 
in  the  saucer  from  time  to  time,  keeping  it  in  a  com- 
fortable living  room  in  a  dark  corner.  After  a  few 
weeks  a  number  of  greenish  bodies  will  be  seen  on 
the  brick.  These  have  been  produced  by  the  ger- 
mination of  the  spores. 

196.  Another  form  or  generation  of  the  fern. — 
The  bodies  produced  by  the  germination  of  the  spores 
are  like  small  irregular  leaves,  and  they  are  seen  to 
adhere  to  the  brick  by  means  of  hairs  or  rhizoids, 
which  serve  the  purpose  of  fixing  and  absorbing 
organs.  Now  these  flat  bodies  must  be  fern  plants 
because  they  came  from  the  spores  of  a  fern.  Theu' 
relation  to  the  ordinarily  known  form  may  be  as- 
certained if  the  culture  is  kept  in  order  for  a  few 
weeks   longer.     Small    upright    stalks   will    appear, 


142  THE  NATURE  AND    WORK  OF  PLANTS 

bearing  a  minute  leaf  which  gradually  enlarges 
until  it  resembles  that  of  the  plant  from  which  the 
spores  were  taken.  A  root  may  also  be  found.  This 
young  plant  is  attached  to  the  leaflike  body  and 
apparently  sprang  from  it.  The  young  plant  with  a 
stem  will  enlarge,  and  if  placed  in  the  soil  it  would 
develop  spores  like  those  which  were  placed  on  the 
brick,  and  the  life  history  of  the  species  would  be 
complete. 

197.  Alternation  of  generations.  —  In  the  complete 
life  of  the  fern  it  is  found  to  develop  two  indi- 
viduals entirely  different  in  form,  and  each  gives 
rise  to  the  other.  This  is  known  as  the  alternation 
of  generations.  One  generation  is  constructed  with 
a  root,  stem,  and  leaves,  and  it  develops  single 
spores  which  are  capable  of  giving  rise  to  the  other 
generation.  This  large  plant  which  is  known  to  the 
ordinary  observer  is  the  sporopliyte.  The  other  gen- 
eration is  a  thallus,  or  prothallus,  and  the  body  con- 
sists of  a  thin  sheet  of  cells  bearing  green  color,  and 
furnished  with  rhizoids  for  absorption  and  fixation. 
This  generation  develops  two  kinds  of  reproductive 
cells  in  little  flasks  on  the  lower  side  of  the  pro- 
thallus.    The    flasks   containing    the    male  gametes 


THE   WAY  IN    WHICH  NEW  PLANTS  ARISE       143 

(§  193)  burst,  and  these  elements  find  their  way  to  tlie 
other  flaslis  where  tlie  female  gametes  are  developed, 
and  one  male  gamete  fuses  with  the  female  gamete, 
and  the  new  cell  thus  formed  gives  rise  to  an  indi- 
vidual of  the  other  generation,  which  is  the  common 
fern  plant.  The  prothallus  form  of  the  fern  is  then 
the  gametojjJiyte.  In  the  fern  the  sporophytic  gen- 
eration is  seen  to  be  much  the  larger,  and  the  higher 
one  follows  the  development  of  the  plant  kingdom 
the  greater  will  be  the  size  of  the  sporophyte,  and 
the  smaller  will  be  the  gametophyte.  On  the  other 
hand  the  gametophyte  attains  greater  importance 
in  some  of  the  lower  forms,  as  may  be  seen  in  the 
moss. 

198.  TJie  two  generations  of  the  moss.  —  Secure 
a  clump  of  a  large  moss,  some  of  the  specimens  of 
which  may  be  seen  to  be  in  "  fruit."  Examine  one 
of  the  specimens  which  is  not  in  "fruit."  It  will 
be  found  to  consist  of  a  small  leafy  stem,  with  per- 
haps rootlike  organs  arising  from  the  lower  end  and 
furnished  with  rhizoids  for  absorption.  The  upper 
extremity  of  the  stems  bears  leafy  cups,  in  which  are 
the  organs  containing  the  two  kinds  of  gametes.  This 
is  the  gametophyte  of  the  moss.     The  male  gametes 


144  THE  NATURE  AND    WORK  OF  PLANTS 

fuse  with  the  female  gametes,  as  m  the  fern,  and  the 
cell  formed  germinates  without  leaving  its  place  as 
in  the  fern,  but  the  structure  of  the  individual 
formed  is  very  much  different.  The  second  genera- 
tion consists  of  a  slender  brownish  or  greenish  stem, 
bearing  a  large  capsule.  This  capsule  is  composed 
of  tissue  which  contains  chlorophyl,  is  furnished 
with  a  hood  or  other  appendages,  and  contains  a 
flask  or  sac,  the  contents  of  which  develop  into 
spores.  The  spores  germinate  and  form  the  leafy 
stemmed  plants  examined  at  first,  and  the  capsule 
and  its  stalk  are  thus  the  sporophyte  of  the  moss. 
It  is  seen  to  be  able  to  form  some  of  its  food  by 
means  of  its  chlorophyl,  but  it  is  dependent  upon 
the  gametophyte  for  its  supply  of  water  and  mineral 
salts,  and  is  sometimes  said  to  be  parasitic  upon  it. 

199.  Occurrence  of  generations. — This  alterna- 
tion of  the  two  generations  of  a  species  is  not  inva- 
riable. It  was  found  that  by  vegetative  methods 
of  reproduction  (§  180)  the  cutting  reproduces  its 
own  generation  in  all  the  experiments  tried.  There 
are  some  instances,  however,  where  the  cutting  of  a 
sporophyte  will  produce  a  gametophyte,  and  vice 
versa.     Then,  again,  the    spores   developed    by   the 


THE   WAY  IN   WHICH  NEW  PLANTS  ARISE       145 

sporophyte  often  grow  into  sporophytes  upon  ger- 
mination. This  is  found  in  mushrooms  and  moulds. 
The  mould  which  grows  upon  moist  bread  develops 
small  sacs  filled  with  spores,  which  take  a  black  or 
brown  color  when  ripe.  These  spores  germinate 
and  grow  individuals  exactly  like  those  from  which 
they  sprung,  without  the  formation  of  another  gen- 
eration. The  asexual  spores  of  the  sporophyte  may 
be  observed  if  the  umbrella-like  top  of  a  mushroom 
is  carefully  taken  off  and  placed  on  a  sheet  of  white 
paper  for  a  day  or  two.  The  spores  which  are  borne 
on  the  thin  plates  or  gills  on  the  under  side  of  the 
cajj  are  set  free  and  fall  upon  the  paper  in  great 
number.  The  germination  of  these  generally  pro- 
duces a  sporophyte. 

200.  The  generations  of  the  seed  plants.  —  The 
species  which  produce  flowers  and  seeds  have  two 
generations,  but  the  gametophyte  is  so  small  that 
its  behavior  may  not  be  seen  without  the  use  of 
special  methods  of  observation  with  the  compound 
microscope. 

201.  The  gametophyte,  or  egg-hearing  generatio7i 
in  the  seed  plant.  —  It  was  shown  in  the  life  history 
of  the  fern  that  unlike  cells  from  different  parts  of 


146  THE  NATURE  AND    WORK  OF  PLANTS 

the  body  of  the  gametophyte  were  united  to  form 
the  fertilized  egg  from  which  a  new  plant  was 
formed,  though  this  is  not  always  the  case.  In  the 
seed  plants,  however,  the  two  kinds  of  gametes  are 
produced  on  different  individuals,  which  are  borne 
on  separate  organs  of  the  sporophyte,  or  on  sepa- 
rate plants.  Thus  the  male  gamete  is  produced  in 
a  minute  individual  formed  by  the  germination  of 
the  pollen,  and  the  female  gamete  in  another  im- 
bedded deeply  in  the  ovary. 

202.  The  structure  of  a  floiver.  —  Secure  a 
fresh  supply  of  flowers  of  the  apple.  This  may 
be  done  in  winter  by  bringing  in  some  twigs 
of  these  trees,  in  the  latter  part  of  the  winter, 
and  placing  the  lower  ends  in  water  for  two  or 
three  weeks  before  needed.  The  preparation  should 
be  kept  in  a  comfortable  living  room  near  a  win- 
dow. A  supply  of  these  or  other  suitable  species 
may  be  found  out  of  doors  during  the  proper  sea- 
son. When  the  fully  opened  blossoms  have  been 
secured,  note  that  the  flower  appears  to  sit  in  a 
cup  the  upper  edges  of  which  divide  into  five  leaf- 
like bodies.  The  shape,  size,  and  arrangement  of 
these    will    vary    greatly    in    the    several    species 


THE   ]VAY  IN   WHICH  NEW  PLANTS   ARISE       147 

selected  for  observation.  The  separate  parts  of 
this  cup,  or  circle,  are  usually  termed  sepals,  and 
while  they  serve  important  uses  in  protecting  other 
parts  of  the  flower,  or  the  fruit,  yet  they  are  not 
essential  to  reproduction,  and  are  lacking  in  many 
species.  Immediately  inside  the  sepals  is  a  circle 
of  five  large  colored  leaves,  forming  the  most 
showy  part  of  the  flower;  these  are  the  ^:>e^'«fe. 
Like  the  sepals,  they  also  exhibit  great  diversity 
in  number,  size,  shape,  and  color  in  different  species. 
Some  are  most  beautifully  painted  and  marked, 
and  it  is  principally  to  the  development  of  these 
organs  in  various  plants  that  the  florist's  art  is 
directed.  These  organs,  also,  play  only  a  minor 
part  in  reproduction,  and  are  lacking  in  many 
species. 

Immediately  inside  the  petals  are  to  be  seen  a 
number  of  small  knobs,  or  flasks,  not  much  larger 
than  a  pin's  head,  borne  on  curved  stalks.  These 
are  the  stamens,  and  if  the  flasks  are  crushed  or 
torn  open,  they  will  be  found  to  contain  a  yellow- 
ish powder  made  up  of  a  great  number  of  j^ollen 
grains.  In  the  centre  of  the  flower  are  five  small 
stalks  extending  up  into  the  air,  the  styles.  The 
expanded  surface  of   the  tip  are  the  stigmas.     The 


148  THE  NATURE  AND   WORK  OF  PLANTS 

lower  end  of  these  styles  terminates  in  a  capsule 
buried  in  the  tissues  at  the  base  of  the  flower. 
This  capsule,  if  carefully  cut  across  with  a  sharp 
knife,  will  be  found  to  be  divided  into  five  cham- 
bers, correspondent  to  the  number  of  styles,  and  it 
is  termed  the  ovary ^  because  it  is  in  this  organ  that 
eggs  are  formed.  The  ovary,  styles,  and  stigma  con- 
stitute the  ^:)^s^^7. 

Almost  any  flower  will  suffice  for  observations 
of  the  above  character.  A  dozen  or  more  different 
kinds  should  be  examined,  noting  the  number,  size, 
and  arrangement  of  the  different  organs.  The 
greatest  diversity  will  be  found,  indicating  that 
the  separate  species  accomplish  the  work  of  re- 
production in  a  manner  characteristic  of  them- 
selves. 

The  flower  described  above  is  said  to  be  perfect, 
but  in  others  the  stamens  and  pistils  are  in  separate 
flowers  on  the  same  or  different  individuals.  The 
petals  or  the  sepals  may  be  absent  or  replaced  by 
circles  of  bracts.  What  is  the  arrangement  of  the 
organs  in  the  jack-in-the-pulpit,  spring  beauty,  but- 
tercup, the  ash  tree,  willow,  beech,  maple,  and  oaks  ? 
Examine  also  the  flowers  of  the  lily,  trill ium,  lark- 
spur, bean,  and  geranium. 


TUE   WAY  IN   WHICH  NEW  PLANTS  ARISE       149 

203.  Spores  of  seed  jjlants.  —  The  sporopliytes  of 
seed  plants  produce  two  kinds  of  spores.  One  is 
formed  in  the  stamen  and  forms  the  pollen  grains, 
and  the  other  grows  in  the  ovary  and  produces  the 
gametophyte  which  bears  the  egg  cells. 

204.  Pollination.  —  In  order  to  complete  the 
life  history  of  the  plant  it  is  necessary  that  the 
pollen  grains  should  be  transported  to  the  stigmas, 
or  upper  extremities  of  the  pistils,  where  they  may 
germinate  and  send  a  long  tube  down  to  the 
ovaries.  Furthermore,  it  is  important  in  a  great 
number  of  species  that  the  pollen  from  one  plant 
should  be  carried  to  the  pistils  of  another,  a  pro- 
cess termed  by  the  botanist  cross  2^ollination.  The 
seeds  and  seedlings  obtained  by  this  method  are 
much  stronger  and  represent  the  species  more  per- 
fectly in  most  instances  than  those  which  result  from 
the  action  of  the  pollen  upon  the  pistil  of  the  same 
flower.  The  various  devices  by  which  this  cross 
pollination  is  secured  are  almost  without  number. 
One  method  by  which  the  pollen  of  any  flower 
is  kept  from  its  own  pistil  is  to  have  the  stamens 
and  pistil  mature  at  different  times.  In  other 
cases   the   stamens   are    below    the   pistils,   so    that 


150  THE  NATURE  AND    WORK  OF  PLANTS 

the  pollen  would  fall  away  from  instead  of  upon 
the  pistil  of  the  same  flower.  Having  guarded 
against  self-pollination,  the  plant  must  next  be  pro- 
vided with  means  of  securing  pollen  from  other 
flowers  for  all  the  pistils.  The  principal  agencies 
which  it  makes  use  of  in  this  work  are  the  wind 
and  animals,  principally  insects. 


205.  T7ie  ivind  as  an  aid  to  pollination.  —  More 
than  ten  thousand  species  are  known  to  make  use 
of  the  wind  as  an  agency  in  carrying  the  pollen  from 
one  flower  to  another.  In  order  to  do  this  success- 
fully great  quantities  of  pollen  are  produced  and 
thrown  into  the  air  upon  the  opening  of  the  pollen 
sacs,  and  then  float  upon  the  currents  of  air,  some  of 
them  alighting  upon  the  stigmas  of  other  flowers. 
The  pines,  oaks,  beeches,  hazels,  birches,  poplars, 
walnuts,  mulberries,  and  some  maples  throw  their 
pollen  into  the  air  and  allow  it  to  float  to  other 
flowers  in  this  manner.  It  is  a  matter  of  common 
knowledge  that  when  a  single  row  of  corn  is  planted 
in  a  field  with  no  other  collection  of  the  same  in  the 
vicinity,  generally  no  seeds  are  produced.  This  will 
always  be  the  case  if  the  row  is  at  right  angles  to  the 
prevailing  winds.     The  pollen  of  the  pines  is  often 


THE   WAY  IN   WHICH  NEW  PLANTS  AIIISE       151 

thrown  into  the  air  in  such  quantities  that  it  is 
deposited  upon  the  ground,  making  a  "  shower  of 
sulphur." 

206.  Animals  as  I'^ollen  carriers.  —  The  flowers 
of  many  species  are  provided  with  means  of  attrac- 
tion to  certain  animals,  principally  insects,  and  dur- 
ing their  visits  pollen  adheres  to  their  bodies  and 
is  carried  to  the  next  flower.  The  attraction  may 
be  nectar  or  honey,  the  pollen  itself,  a  place  for 
the  deposit  of  eggs,  or  the  flower  may  offer  the 
insect  a  suitable  place  of  refuge  or  lodgment  for 
the  night  or  during  a  storm.  The  description  of 
the  various  methods  by  wdiich  this  is  done  would 
fill  a  large  book,  and  may  not  find  place  here.  On 
a  favorable  day  in  the  spring  or  summer  the  student 
should  find  a  flower  which  is  frequented  by  insects, 
and  note  the  manner  in  which  this  visit  is  made. 
First  determine  the  object  of  the  visit.  Then  note 
what  parts  of  its  body  rub  against  the  stamens  and 
pistils.  Catch  one  of  the  insects,  and  examine  its 
body  for  traces  of  pollen.  Examine  a  number  of 
flowers  late  in  the  evening  or  early  in  the  morning 
for  animals  which  have  lodged  in  them  during 
the  night. 


152  THE  NATURE  AND    WORK  OF  PLANTS 

207.  Fertilization.  —  When  the  pollen  is  carried 
to  the  flower  which  it  may  benefit,  it  can  only  be  of 
use  if  it  is  deposited  on  or  near  the  stigma  at  the  top 
of  the  pistil.  Here  it  finds  a  sweetish  and  sticky 
substance  made  up  of  cane  sugar  and  ghicose  which 
it  uses  as  food  in  any  growth  it  may  make.  If 
properly  placed  on  this  stigma,  the  presence  of  this 
sweetish  substance  starts  it  to  germinating.  A  long 
slender  tube  is  produced,  making  a  structure  much 
as  if  the  head  of  a  pin  were  to  grow  out  and  form 
the  body  of  the  pin.  The  pollen  tube  is  generally 
very  crooked  and  it  bores  into  the  sticky  substance 
in  which  the  pollen  grain  is  imbedded,  and  then 
grows  down  into  the  style  in  an  effort  to  get  away 
from  the  oxygen  of  the  air.  Not  only  does  it  strive 
to  get  away  from  the  oxygen  of  the  air,  but  certain 
substances  in  the  ovary  attract  it.  Now  the  tube 
formed  by  the  grain  or  pollen  is  a  part  of  a  gameto- 
phyte,  and  near  its  tip  it  contains  a  minute  mass  of 
protoplasm,  which  is  the  male  gamete  which  is  to 
be  carried  to  the  egg.  The  embryo  sac  in  the 
ovary  contains  the  female  gametophyte  bearing  an 
egg  cell,  and  the  pollen  tube  extends  to  it,  carry- 
ing the  male  gamete  in  its  own  tip.  The  union  of 
the  gamete   from  each  constitutes  fertilization,  and 


THE   WAY  IN   WHICH  NEW  PLANTS  ARISE       153 

the  result  is  a  structure  from  which  a  new  sporo- 
phyte  is  formed.  The  ovary  may  be  compound  and 
contain  many  embryo  sacs,  in  which  case  a  separate 
pollen  tube  will  be  necessary  to  fertilize  each  one. 
The  result  will  be  many  seeds  or  embryos  separate 
or  in  a  many-seeded  fruit.  The  growth  of  the  pol- 
len tube  down  through  the  pistil  to  the  embryo  sac 
may  take  only  a  few  hours,  or  it  may  occupy  a  year, 
as  in  the  pines.  Shortly  after  the  fertilization  of  the 
egg  it  begins  to  grow  and  divide  until  an  embryo 
plant  of  the  sporophytic  generation  is  formed,  hav- 
ing possibly  a  root,  a  stem,  and  one,  two,  or  more 
seed  leaves  with  the  main  growing  point  of  the 
future  stem. 


VIII.    SEEDS  AND  FRUITS 

208.  The  seed. — After  the  embryo  has  reached 
a  certain  stage  of  development  it  becomes  quiescent 
and  remains  so  until  the  time  and  opportunity  ar- 
rives for  it  to  grow  in  the  germination  of  the  seed. 
During  the  development  of  the  embryo  from  the  egg, 
reserve  foods  for  its  use  during  germination  in  the 
shape  of  oil,  starch,  sugar,  or  j^rotei?!  may  be  depos- 
ited in  its  seed-leaves,  or  in  the  seed-coats,  or  in  other 
organs  developed  for  that  purpose. 

209.  The  existence  of  the  seed.  —  Generally  about 
the  time  that  the  embryo  has  completed  growth  and 
the  deposit  of  food  has  been  made,  the  seed  or  fruit 
is  separated  from  the  parent  plant,  though  this  is 
not  always  the  case.  Germination  of  the  seed  takes 
place  when  it  secures  proper  conditions  of  season, 
tnoisture,  and  temjjeratiire.  This  may  be  in  a  few 
days  or  several  years.  Some  seeds  actually  grow 
before  separation  from  the  parent  plant,  while  others 
may  remain  quiescent  during  the  lifetime  of  a  man. 


SEEDS  AND  FRUITS  155 

Stories  are  current  of  seeds  being  taken  from 
mummy  cases  six  thousand  years  old  v/liicli  showed 
powers  of  germination,  but  such  statements  are  not 
authentic.  Instances  are  known  in  which  certain 
species  have  lived  three  hundred  or  even  four  hun- 
dred years,  but  these  probably  represent  the  limit 
attainable  by  only  a  few  plants.  Ordinary  forms, 
such  as  wheat  and  corn,  may  not  live  longer  than 
fifteen  or  twenty  years  at  the  utmost,  and  the 
seeds  of  nearly  all  cultivated  plants  begin  to  show 
lessening  powers  of  germination  after  a  year. 
Some  are  totally  worthless  the  second  year. 

210.  Fruits.  —  In  addition  to  the  coats  formed 
around  the  seed  the  portions  of  the  ovary  in  con- 
tact with  the  seed  are  often  developed  in  certain 
ways  of  benefit  or  assistance  in  the  protection,  dis- 
semination, or  germination  of  the  seeds.  The  seed 
and  all  of  the  parts  of  the  ovary  adhering  to  it 
constitute  a  fruit.  The  study  of  the  structure  and 
behavior  of  the  fruit  after  the  ripening  of  the  seed 
will  therefore  be  of  great  interest. 

211.  The  cocoanut.  —  The  fruit  of  Cocos  niici- 
fera  offers  a  most  interesting  object  for  the  illus- 
tration of  the  action  and  structure  of    the  fruit  of 


156  THE  NATURE  AND    WORK  OF  PLANTS 

a  palm.  The  material  necessary  for  the  work  con- 
sists of  a  few  stripped  nuts,  such  as  are  offered  for 
sale  in  every  village,  and  some  from  which  the 
husks  have  not  been  taken.  The  latter  may  be 
obtained  from  merchants  dealing  extensively  in 
tropical  fruits. 

Two  or  more  each  of  the  whole  fruits,  and  the 
same  number  of  stripped  nuts,  should  be  placed  in 
moist  sawdust  or  soil  in  a  box  two  or  three  times 
its  size,  and  kept  in  a  comfortable  living  room  or 
greenhouse  if  the  work  is  to  be  done  in  winter. 
In  the  summer  it  may  be  placed  in  the  ground 
like  any  seed.  The  time  necessary  for  germination 
is  from  six  to  ten  weeks.  This  will  furnish  ger- 
minated seeds  for  examination,  and  will  also  show 
whether  the  husk  is  necessary  for  germination  or  not. 

I.  Size  and  appearance  of  the  fruit. 

Make  an  examination  of  the  entire  fruit,  and 
note :  — 
a.  The  shape  of  the  base  and  apex,  and  gen- 
eral form  of  fruit.  Three  wide  short 
tracts  may  be  found  adhering  to  the 
base ;  these  are  from  the  envelopes  of 
the  flower,  and  may  be  the  calyx.     The 


SEEDS  AND  FRUITS  157 

blunt  angles  may  be  seen  to  run  from 
the  base  to  the  apex.  Draw. 
b.  Measure  the  circumference,  length,  and 
diameter.  Place  in  a  bucket  of  water. 
Does  it  float?  Will  the  stripped  nut 
float?  Plunge  the  fruit  into  a  bucket 
exactly  filled  with  water.  Remove  and 
refill  the  bucket.  The  amount  of  water 
necessary  to  refill  the  bucket  will  be  the 
volume  of  the  fruit.  Many  of  the  fruits 
drop  from  the  trees  into  tlie  water  of 
streams,  ponds,  and  tides,  and  are  carried 
long  distances  before  they  lodge  and  ger- 
minate. The  planters  place  the  fruits  in 
the  margins  of  salt  lagoons  and  marshes, 
and  the  salt  is  supposed  to  hasten  the 
process  of  germination. 

II.  Structure. 

Cut   through   a   fruit   crosswise   by  means  of  a 
sharp  saw,  and  note  :  — 
a.   The  husk,  the  outer  layer  of  which  is  smooth 
and  firm,  while  the  mass  is  composed  of 
strong  fibres  and  2^ith.     Observe  the  at- 
tachment of  the  husk  to  the  shell. 


158  THE  NATURE  AND    WOEK  OF  PLANTS 

h.  Strip  the  husk  from  the  entn^e  fruit,  and 
note  its  rehitive  thickness  over  different 
parts  of  the  shelh  Note  also  the  charac- 
ter of  the  fibres  at  the  basal  end.  The 
husk  is  derived  from  the  wall  of  the 
ovary.  If  the  fruit  were  suspended  on 
its  stem  and  were  broken  off  suddenly, 
which  end  would  strike  the  ground  first  ? 
Do  you  think  this  beneficial  or  not  ? 
Examine  the  stripped  nut  and  note  : — 

c.  The  shape  and  markings  of  the  shell.     The 

three  dark  circular  areas  on  the  basal  end 
are  the  marks  of  the  three  parts  or  car- 
pels of  the  ovary. 
Break  or  cut  up  the  nut  and  test  — 

d.  The  hardness  of  the  shell.     Cut  with  knife 

and  test  strength.     Is  it  "  air  tight  "  and 
"  water  tight "  ? 

The  husk  is  derived  from  the  outer 
wall  of  the  ovary,  and  the  shell  from  the 
inner  wall,  neither  being  seed-coats. 

III.   Tlie  seed. 

Examine  the  nut  which  has  been  cut,  and  note :  — 
a.  The  central  cavity,  filled  with  a  sweetish 


SEEDS  AND   FRUITS  159 

clear  fluid,  the  "  milk."  Determine  the 
capacity  of  this  central  cavity. 

h.  The  white  layer  of  "  meat,"  the  endosjjerm, 
which  is  composed  of  storage  cells  con- 
taining reserve  food.  Apply  a  drop  of 
iodine  as  a  test  for  the  presence  of 
starch.  The  endosperm  plainly  con- 
tains oil,  for  it  is  expressed  in  great 
quantities  in  factories.  Sugar  may  be 
detected  by  the  taste.  Split  off  por- 
tions of  the  endosperm  and  measure  its 
thickness. 

c.  A  brownish  membrane  will  be  seen  adher- 
ing to  the  outer  surface  of  the  endo- 
sperm, which  is  made  up  of  the  true 
seed-coats. 

IV.   TJie  embryo. 

Working  from  the  inside,  carefully  cut  away  the 
endosperm  from  around  the  eyes. 
a.  Under  one  of  them  will  be  found  an  irreg- 
ular white  cylinder,  about  a  third  of  an 
inch  long,  with  the  outer  flattened  end 
pressed  against  the  seed-coat,  and  the 
inner  portion  buried  in  the  endosperm. 


160  THE  NATURE  AND   WORK  OF  PLANTS 

This  is  the  young  plantlet.  There  was 
originally  an  egg  apparatus  under  each 
eye,  but  two  of  them  have  not  been 
given  an  opportunity  for  development, 
and  the  whole  ovary  is  devoted  to  the 
nourishment  and  protection  of  one  em- 
bryo. Rarely  two  embryos  are  per- 
fected in  one  fruit,  making  twin  trees 
when  they  germinate.  Make  a  drawing 
of  the  embryo. 

V.  Germination. 

Carefully  cut  away  one  side  of  the  germinated 
fruit,  being  careful  not  to  injure  the  young 
plant,  and  note :  — 
a.    The  absorbing  organ,  the  inner  end  of  the 
embryo,  which  is  made  of  the  cotyledon, 
has    developed   a   mass   of   tissue,  very 
much  the  shape  of  a  puff-ball,  which  is 
at  first  the  size  of  a  marble,  but  which 
gradually  enlarges  until  it  fills  the  cav- 
ity of   the   nut.     It  uses  the  milk   for 
food   as   it   grows,   and   furthermore  it 
secretes  digestive  fluids  (enzyms),  which 
dissolve  the  starch  and  oil  in  the  endo- 


SEEDS  AND  FRUITS  161 

sperm,  about  as  it  would  be  done  in  the 
human  stomach.  The  fluid  thus  ob- 
tained is  conveyed  back  into  the  young 
plant  and  serves  as  food.  The  endo- 
sperm may  be  seen  to  be  thinner  where 
the  absorbing  organ  has  touched  it. 
The  amount  of  food  furnished  by  the 
endosperm  is  so  great  that  the  plantlet 
may  be  nourished  many  months  from  it 
alone,  and  generally  it  is  entirely  con- 
sumed, remaining  sweet  and  sound  as 
long  as  a  trace  is  present. 
The  outer  end  of  the  cylindrical  part  of  the 
embryo  contains  the  plumule,  or  young 
shoot  of  the  plant,  and  the  root,  which 
pushes  through  the  eye,  breaking  the  thin 
layer  of  the  shell  at  that  point,  when 
the  plumule,  a  conical  mass  of  firm 
leaves,  bores  upward  through  the  fibres  of 
the  husk.  When  light  is  reached,  green 
leaves  are  formed. 

The  main  root  goes  downward,  send- 
ing out  branches  which  break  through 
the  husk  at  various  points,  finally  pene- 
trating; the  soil.     If  the  fruits  have  been 


162  THE  NATURE  AND    WORK  OF  PLANTS 

germinated  in  the  spring,  the  plantlets 
may  endure  the  summer  out  of  doors  in 
almost  any  part  of  the  United  States. 

The  cocoanut  has  its  original  habitat 
in  the  Eastern  hemisphere,  but  now 
occupies  the  tropics  around  the  globe. 
This  wide  distribution  has  been  secured 
by  the  agency  of  wind  and  water,  and 
by  the  attractive  power  of  the  food, 
stored  up  in  the  endosperm,  for  tribes  of 
savage  and  civilized  men. 

212.  The  date.  —  The  fruit  of  the  commercial  date 
may  be  easily  obtained,  and  used  to  illustrate  the 
action  of  the  fruit  of  a  second  palm. 

Secure  a  few  dozen  dried  dates,  such  as  are  sold 
by  grocers  and  confectioners,  and  place  a  dozen  in 
the  soil  in  a  pot  kept  at  a  temperature  about  equal 
to  that  of  a  comfortable  living  room,  three  or  four 
weeks  before  the  observations  are  to  be  begun. 
Strip  the  fleshy  part  of  the  fruit  of  a  second  dozen 
and  put  in  a  second  pot  and  place  with  the  first. 
This  will  show  whether  the  edible  flesh  is  of  any 
benefit  in  the  actual  process  of  germination.  Soak 
another  lot  in  water  for  two  weeks  for  dissection. 


SEEDS  AND  FRUITS  163 

I.  The  appearance  of  the  fruit. 

Place  some  of  the  fruits  in  water  for  an  hour, 
and  then  note  :  — 
a.  The  general  appearance,  size,  and  form. 
h.  The  outer  covering ;  is  it  a  distinct  mem- 
brane, or  a  part  of  the  flesh  underneath, 
as  in  tlie  husk  of  the  cocoanut  ? 
c.  The  edible,  fleshy  portion ;  is  it  attached  to 
the  seed  ? 

IT.   Tlieseed. 

a.  Describe  the  form  of  the  seed. 

h.  Test  the  hardness  and  brittleness  of  the 
seed  and  its  coats.  Crush  or  break  the 
seed  to  determine  its  firmness. 

c.  Cut  away  the  coats  from  the   surface  of 

the  seed  opposite  the  groove,  and  note 
the  position  of  the  tip  of  the  main  root 
of  the  embryo. 

d.  Cut  the  seed  across  and  take  out  the  em- 

bryo.    Describe  its  form  and  draw. 

III.   Germination. 

Cut  across  some  of  the  germinating  seeds  in  the 
same  manner,  and  note:  — 
a.  Ahsorhing  organ,    the    cotyledon,    here  as 


164  TEE  NATURE  AND   WORE  OF  PLANTS 

in  the  cocoanut,  serves  as  a  digesting 
and  absorbing  organ.  It  develops  as 
a  cylindrical  mass,  and  its  juices  corrode 
the  hard  cellulose  of  the  seed  which  is 
stored  as  food  for  the  young  plantlet. 
The  absorbing  organ  expands  until  it 
consumes  all  of  the  cellulose,  and  finally 
fills  up  the  entire  space  inside  the  coats. 
b.  Sketch  the  development  of  the  basal  end 
of  the  cotyledon.  It  elongates  and 
forces  the  embryo  stem  tipped  with  the 
root  downward  through  the  soil.  As  it 
does  so  it  opens  at  one  side  and  allows 
the  first  green  leaf  of  the  plumule  to 
come  out.  Finally  the  root  begins  to 
develop,  and  it  continues  the  downward 
course  taken  by  the  cotyledon.  If  the 
seeds  were  in  the  dry  soil  in  which 
the  plant  grows,  the  root  and  cotyledon 
would  bore  down  more  than  a  yard  be- 
fore any  branches  would  be  given  off. 
But  in  the  pot  cultures  this  is  impossi- 
ble and  unnecessary,  for  the  plant  finds 
sufficient  moisture  near  at  hand.  So  far 
as  can  be  found  from  an  examination  of 


SEEDS  AND  FBUITS  165 

the  date  seed,  without  seeing  the  plant 
in  its  native  habitat,  the  only  manner  in 
which  this  fruit  would  secure  the  dis- 
semination of  the  seed  would  be  by 
means  of  its  pleasant  tasting  fruit, 
which  would  cause  it  to  be  sought  for 
food  by  animals  in  general,  some  of 
which,  including  man,  in  using  it  would 
carry  the  fruit  some  distance  from  the 
parent  tree.  This  use  of  the  fleshy 
portion  for  food  does  not  in  any  way 
affect  the  germinating  power  of  the  seed, 
so  long  as  it  is  not  cooked.  Further- 
more, the  seeds  are  capable  of  enduring 
great  extremes  of  heat  and  cold,  and 
may  lie  around  on  the  surface  of  the 
soil  for  months  or  even  years,  and  then 
grow  when  the  proper  conditions  for 
germination  are  given  them. 

213.  Maize,  or  Indian  corn.  —  Maize,  or  the  ordi- 
nary Indian  corn,  is  a  third  example  of  the  plants 
belonging  to  the  same  general  group  as  the  palms, 
and  it  is  even  more  interesting  than  the  fruits 
just    examined.     In   order   to   see   clearly  the   pur- 


166  THE  NATURE  AND    WORK  OF  PLANTS 

poses  and  nature  of  these  fruits,  one  should  have 
some  entire  ears  which  have  been  brought  in  with 
the  husk  and  are  still  attached  to  the  stalk,  or,  at 
least,  a  section  of  it. 

I.   The  arrangement  and  protection  of  the  fruits. 
Examine  the  external  characters  of  the  ear  and 
its  covering,  and  note  :  — 
a.   The  silks,  hanging  in  a  reddish-brown  tuft 

from  the  tip. 
h.  The  texture  of  the  husks,  and  the  manner 
in  which  they  cover  the   ear.     Remove 
one  at  a  time,   and  compare  the  outer 
and  inner  husks. 

c.  Take   one    of   the    "  silks,"    and  follow  it 

to  its  inner  end.  To  what  is  it  at- 
tached ? 

d.  The  great  number  of    fruits  arranged  in 

parallel  rows  on  the  central  stalk  or 
'^  cob."  Estimate  the  number  of  the 
grains. 

e.  The  attachment  of  the  grain  to  the  cob. 

The  scales. 
/.  The  cob.     Cut  or  break  it  across,  and  de- 
scribe its  structure. 


SEEDS  AND  FRUITS  167 

II.  The  grains  or  seeds. 

Place  a  number  of  seeds  in  moist  earth  ten  days 

before  the  observations  are  to  be  made,  and 

a  few  in  water  a  day  beforehand.     Examine 

the  soaked  seeds,  and  note  :  — 

a.  The  forms,  size  and  outward  appearance. 

Compare  the  two  broader  sides. 
h.  Remove  the  outer  membrane  which  covers 
the  seed.  This  is  composed  not  only  of 
the  two  seed-coats,  but  also  of  layers 
from  the  walls  of  the  ovary,  which  it 
would  be  impossible  to  separate  without 
the  use  of  methods  which  need  the  com- 
pound microscope. 

c.  The  seed   is  composed  of   two  parts :   the 

embryo,  which  occupies  the  space  under 
the  whitish  area  on  one  side,  and  the 
mass  of  endosperm,  or  stored  food. 

d.  Examine  the  endosperm,  and  test  with  a 

drop  of  iodine.  It  is  this  portion  of  the 
grain  that  is  chiefly  used  for  food  by  man. 

III.   The  embryo. 

Remove   the    entire    embryo   from    a   softened 
grain,  and  note  :  — 


168  THE  NATURE  AND    WORK  OF  PLANTS 

a.  Its  general  shape.     Sketch. 

b.  The   scutellum,    or    absorbing    organ,   the 

part  which  lies  under  the  embryo  and 
in  contact  with  the  endosperm.  If  ger- 
minated seeds  are  examined,  this  organ 
will  be  seen  to  have  enlarged  and  taken 
up  some  of  the  endosperm,  as  in  the  date 
or  cocoanut.  It  has  the  power  of  se- 
creting digestive  fluids,  which  dissolve 
starch  and  convert  it  into  sugar.  The 
action  of  this  fluid  on  the  endosperm 
soon  causes  it  to  become  soft,  and  then 
milky  fluid. 

c.  The   young   plantlet   shows    an    unrolling 

leaflet,  a  short  stem,  and  a  main  root. 
Describe  the  action  of  these  organs  in 
germination.  Note  the  formation  of 
young  roots  above  the  base  of  the  main 
roots.  These  are  the  stilt  roots,  which 
are  so  prominent  on  the  full-grown 
plant  (§  29). 

IV.  Endurance  of  the  seeds. 

Put  a  number  of  sound  grains  into  a  covered 
vessel  full  of  water,  set  on  the  stove,  and 


SEEDS  AND  FRUITS  1C9 

allow  the  water  to  boil.  Place  an  equal 
number  of  grains  on  the  cover  of  the  ves- 
sel, but  where  they  will  be  dry.  Plant 
both  lots  of  seeds  in  the  soil,  and  note :  — 

a.  The   number   that   germinate.      What  do 

you   conclude   as  to   the   power  of   the 
grain  to  resist  extremes  of  heat? 

Put  a  number  of  grains  in  a  shallow 
dish  of  water  in  the  morning,  and  set 
outside  where  they  may  freeze  at  night. 
Place  alongside  these  an  equal  number 
in  a  dry  dish.  Now  put  both  lots  in 
separate  boxes  of  moist  soil,  keep  in  a 
comfortable  livmg  room,  and  note  :  — 

b.  The  number  germinating.     What  do  3'ou 

conclude  as  to  the  power  of  the  grains 
to  resist  cold  ? 

The  capacity  of  the  seed  to  endure 
heat  or  cold  is  very  great.  The  seed  of 
a  plant  is  capable  of  undergoing  much 
greater  extremes  of  climate  than  the 
adult  plant,  which  is  largely  due  to  the 
fact  that  it  contains  very  little  water. 
Thus  a  seed  if  kept  dry  may  be  exposed 
to  a  heat  which  will  boil  water  and  still 


170  THE  NATURE  AND    WORK  OF  PLANTS 

germinate,  but  if  actually  put  into  boil- 
ing water  and  permitted  to  absorb  the 
warm  liquid,  it  will  be  killed.  On  the 
other  hand,  seeds  of  many  common 
plants  may  be  bathed  in  liquid  hydro- 
gen at  a  temperature  of  four  hundred 
and  twenty  degrees  below  freezing  point 
and  still  retain  the  power  of  germination. 

V.   The  dissemination  of  the  seeds. 

a.  Could  dissemination  take  place  by  water 
or  wind  ? 

h.  If  you  can  observe  a  field  of  corn,  note 
whether  any  animals  carry  away  the 
grains  or  not,  and  if  so  what  is  done 
with  them.  Are  all  of  them  destroyed  ? 
It  would  also  be  interesting  to  make 
similar  observations  on  the  acorns  of 
the  oaks. 

Man  has  been  an  important  factor  in 
the  distribution  of  corn,  and  his  method 
of  growing  and  treating  it  has  resulted 
in  the  development  of  new  species  and 
„ varieties.  It  is  cultivated  over  great 
areas,  and  although  the  larger  number 


SEEDS  AND   FRUITS  171 

of  the  seeds  produced  annually  are  used 
as  food,  yet  enough  are  preserved  to 
perpetuate  the  species,  so  that  this  plant 
is  represented  by  many  millions  of  in- 
dividuals in  regions  where  it  would 
have  none  if  it  were  not  for  man. 
Thus  without  the  interference  of  man 
corn  could  not  grow  and  seed  from  year 
to  year  in  any  place  in  northern  United 
States. 

214.  77ie  fruit  of  the  dot-hur,  Xanthium.  —  The 
fruits  of  this  plant,  which  is  a  relative  of  the  sun- 
flower, are  very  much  different  from  those  previously 
examined,  both  in  structure  and  action.  The  plant 
is  a  weed,  and  it  is  more  or  less  abundant  over  a 
great  part  of  the  United  States.  The  fruits  may 
be  taken  from  the  plant  in  August  or  September, 
picked  up  from  the  ground  or  taken  from  the  coats 
of  animals  in  late  autumn. 

I.  External  ajJj^earcmce  of  fruit. 

Examine  the  clusters  of  four  or  five  fruits,  and 
note  their  position  on  the  plant  as  well  as 
the  following  features  :  — 
a.  The  prongs  at  the  apex,  and  the  hooked 


172  THE  NATURE  AND   WORK  OF  PLANTS 

bristles  over  the  remainder  of  the  fruit. 
Make  a  drawing,  showing  form  and  ar- 
rangement of  bristles. 
h.  Cut  across  the  fruit,  and  note  the  struc- 
ture of  the  outer  walls  which  bear  the 
bristles,  and  that  the  fruit  is  two-seeded. 

II.  The  seeds. 

a.  The  seeds  are  unequal  in  size. 
h.  The  seed-coats  are  distinct  in  texture  and 
color.     Describe. 

III.  The  emhryo. 

a.  The  embryo  seems  to  fill  the  entire  seed. 
The  food  is  stored  up  in  two  oblong 
oval  leaflike  bodies,  the  cotyledons, 
which  are  whitish  in  color. 

h.  The  2^^umide,  or  young  leaves,  may  be 
found  between  the  cotyledons  and  the 
short  main  root  below  them.  Draw 
the  embryo. 

IV.  Germination. 

a.  Examine  twenty  seeds  which  have  lain  in 
moist  soil  for  a  month,  and  from  each 
fruit  generally  but  one  plantlet  will 
have  grown.     Take  up  the  fruit  which 


SEEDS  AND  FRUITS  173 

is  still  attached  to  the  single  germi- 
nated embryo.  The  other  seed  has  not 
shown  any  signs  of  growth. 
h.  Take  a  number  of  these  fruits  from  which 
one  plantlet  has  sprung,  and  put  them 
in  a  pot  and  set  out  of  doors  for  a 
season.  Many  of  them  will  be  found 
to  germinate  the  second  seed. 

c.  Examine  the  young  plant,  and  note   the 

position  and  growth  of  the  cotyledons. 
What  becomes  of  them?  How  does 
the  root  develop?  The  single  cotyle- 
don of  the  species  previously  examined 
did  not  come  out  of  the  seed-coats ; 
what  is  the  behavior  in  this  instance  ? 

d.  Strip    the    seeds    of   several    fruits,  being 

careful  not  to  injure  them,  and  find 
whether  they  will  germinate  alone. 

215.  Nature  of  fruits  of  Xanthium.  —  The  fruits 
of  Xanthium  are  seen  to  be  adapted  for  the  dis- 
semination of  the  seeds  by  becoming  fastened  or 
entangled  in  the  coats  of  animals,  and  thus  are 
carried  long  distances  from  the  parent  plant.  In 
the   case   of   migratory  animals  this  method  might 


174  THE  NATURE  AND    WORK  OF  PLANTS 

carry  them  the  length  or  breadth   of   a   continent, 
across  wide  seas,  or  over  mountain  ranges. 

The  Xanthium  has  an  additional  device  not  found 
on  any  other  known  plant.  This  is  the  manner  in 
which  the  ^;a/re<i  seeds  germinate,  one  the  first  year 
and  the  other  the  second.  This  method  would  enable 
it  to  gain  a  foothold  in  places  where  it  otherwise 
might  not.  Thus,  when  the  fruit  is  carried  to  a 
field  or  dropped  along  the  path  of  the  animal  to 
which  it  has  been  attached,  the  coming  of  the 
spring  season  sets  one  seed  in  action  and  a  plant- 
let  is  produced.  This  may  survive  and  produce  a 
crop  of  fruits,  in  which  case  the  species  will  easily 
hold  its  own  in  this  locality.  On  the  other  hand, 
the  young  plant  may  be  trampled  to  death  by  the 
same  animal  which  brought  it  to  the  place,  it  may 
be  overshadowed  by  other  species  which  grow  more 
luxuriantly,  or  the  watchful  farmer  may  take  this 
opportunity  to  destroy  one  of  the  worst  enemies  of 
his  crops.  The  destruction  of  the  first  seedling 
from  any  cause,  however,  still  leaves  the  species 
another  chance  to  gain  a  foothold  in  this  locality, 
for  at  the  beginning  of  the  second  season  the  other 
seed  germinates  and  begins  the  struggle  for  exist- 
ence for  the  species  all  over  again. 


SEEDS  AND  FEUITS  175 

The  fruit  of  the  Xanthium  then  is  not  only  fur- 
nished with  a  device  for  securing  transportation 
from  any  animal  that  touches  its  fruits,  but  after 
the  fruits  have  reached  a  spot  favorable  for  growth, 
only  half  the  seeds  are  germinated,  the  remainder 
being  held  in  reserve  for  a  second  attempt  which 
may  be  more  successful  than  the  first.  Thus,  if  at 
this  moment  every  plant  of  this  species  were  de- 
stroyed, there  would  still  remain  the  second  seeds  of 
the  fruits  which  have  sent  up  but  one  plantlet  and 
kept  the  other  in  the  form  of  a  seed. 

216.  TJie  apple.  —  The  fruit  of  the  apple  offers 
a  most  interesting  study,  not  only  on  account  of  the 
structure,  but  also  because  of  the  manner  in  which 
it  has  succeeded  in  attracting  the  attention  of  ani- 
mals, particularly  man,  and  has  thus  secured  dis- 
semination over  an  immense  area  of  the  earth's 
surface.  During  this  process  it  has  also  undergone 
great  changes  as  a  result  of  the  methods  of  cultiva- 
tion by  which  it  has  been  grown. 

In  the  examination  of  the  flower  of  the  apple  it 
was  seen  that  the  ovary  was  imbedded  in  a  small 
greenish  capsule,  and  that  the  parts  of  the  flower  ap- 
peared to  stand  on  top  of  it  (§  202).    All  of  the  parts 


176  THE  NATURE  AND    WOBK  OF  PLANTS 

of  a  flower  really  spring  from  the  end  of  the  flower- 
stalk,  so  that  this  young  apple  consists  of  the  bases 
of  the  petals,  sepals,  stamens,  and  pistils  fused  to- 
gether. The  fruit  of  the  apple  is  thus  composed 
of  portions  derived  from  all  of  the  organs  of  the 
flower.  Cut  across  a  mature  apple  in  the  middle, 
and  note  in  the  exact  centre  :  — 

a.  The  core.  —  It  is  seen  to  be  joined  directly  to 
the  stem  at  the  base  of  the  apple,  and  terminates 
at  the  other  end  in  some  small  dried  appendages, 
which  cannot  be  made  out  in  a  ripe  apple.  If  a 
half-grown  specimen  is  secured  fresh  from  a  tree,  it 
will  be  seen  that  the  five  styles  of  the  pistil  are 
attached  to  the  core.  Down  in  the  centre  of  the 
core  will  be  found  five  small  chambers  containing 
seeds;  the  pistil  of  this  plant  was  therefore  com- 
pound, and  each  of  the  five  styles  furnished  a  pas- 
sageway for  pollen  tubes  to  the  egg-cells  in  the 
chambers  at  its  base. 

Make  out  the  7nemhrane  lining  the  seed  cavities, 
or  cells.  Examine  the  flesh  of  the  apple.  Note  the 
outer  skin.  It  is  often  very  strong  and  is  covered 
with  a  layer  of  wax.  What  is  the  difference  between 
the  flesh  of  apples  which  may  be  kept  for  a  long 
time,  and  those  which  rot  shortly  after  they  ripen  ? 


SEEDS  AND   FRUITS  177 

The  membrane  which  lines  the  cavity  of  the  cells 
containing  the  seed  corresponds  to  the  pod  of  a  pea 
m  being  the  wall  of  the  ovary,  and  the  flesh  is  de- 
rived from  the  calyx  and  perhaps  a  part  of  the  stalk. 
The  calyx  and  stamens  are  seen  adhering  to  the  flesh 
in  half-grown  fruits. 

Examine  the  seed  with  respect  to  its  coats  and 
methods  of  germination. 

The  fruit  of  the  apple  attracts  animals  by  the 
food  which  it  offers  them,  and  in  the  use  of  this 
fruit  the  seeds  would  be  carried  some  distance  from 
the  parent  tree.  This  method  operated  both  with 
regard  to  man  and  lower  animals  in  earlier  times. 
Later,  since  man  has  developed  the  art  of  improving 
or  increasing  its  fruit-bearing  capacity  in  order  to 
derive  still  more  benefit  from  it,  the  apple  has 
had  a  very  peculiar  history.  The  edibility  of  its 
fruit  has  still  been  the  attractive  feature,  and  this 
has  secured  the  wide  dissemination  of  the  apple, 
not  by  the  seeds  which  the  fruit  contains,  but  it  has 
induced  man  to  propagate  it  by  means  of  cuttings. 
The  cuttings  are  sometimes  grown  directly  in  the 
soil,  as  in  other  forms  discussed  in  a  previous  para- 
graph. By  a  method  of  grafting,  or  causing  a  shoot 
of   one    tree   to  adhere   and   grow  to   the   body  of 


178  THE  NATURE  AND    WORE   OF  PLANTS 

another,  special  varieties  are  propagated  without 
the  use  of  seed.  The  forms  developed  in  this 
method  are  very  widely  different  from  the  type  of 
the  species,  and  when  a  seed  of  a  fruit  borne  on 
one  of  these  grafted  branches  is  planted,  it  produces 
a  tree  which  is  unlike  the  characteristic  branch  from 
which  it  sprung,  and  it  is  said  not  to  "  come  true." 
As  a  matter  of  fact  the  seedling  does  come  true  to 
the  species,  but  not  to  the  cutting  or  grafted  branch 
from  which  it  sprung. 

217.  The  hean  and  ^jea.  —  Examine  a  flower  of 
the  bean  and  pea.  Note  the  characters  of  the  dif- 
ferent parts  of  the  flower.  Describe  the  number  and 
arrangement  of  the  stamens  and  pistils.  Is  pollina- 
tion aided  by  the  wind  or  animals  ?  Follow  the 
development  of  the  pistil.  From  what  is  the  pod 
derived  ?  Note  the  manner  in  which  the  pods  open, 
and  the  position  of  the  seeds  which  fall  upon  the 
ground.  How  far  are  they  thrown  from  the  parent 
plant  ?     Do  the  pods  open  forcibly  ? 

Describe  and  draw  the  outward  appearance  and 
form  of  the  seeds.  Note  the  number  and  character 
of  the  coats. 

A  number  of  peas  and  beans  should  be  placed  in 


SEEDS  AND  FRUITS  179 

tlie  soil  two  weeks  before  the  observations  are  to  be 
made,  and  a  similar  number  in  a  tumbler  with  damp 
blotting  paper  three  or  four  days  before.  Dissect 
one  of  each  kind  which  has  been  treated  in  the 
latter  way.  The  seed  is  made  up  almost  entirely 
from  two  large  swollen  seed  leaves  or  cotyledons, 
which  readily  separate  when  the  coats  are  removed. 
At  one  side,  holding  the  cotyledons  together,  may 
be  seen  the  young  plant,  consisting  of  the  root,  em- 
hryonic  stem,  and  the  minute  leaves,  or  plumule.  To 
what  part  are  the  cotyledons  attached  ? 

If  the  seeds  which  Avere  placed  in  the  soil  in 
boxes  or  in  the  ground  are  now  observed,  the  be- 
havior of  the  cotyledons  may  be  followed.  Both 
contain  the  reserve  food  for  the  young  plant,  and 
yield  it  as  needed.  What  position  do  the  cotyle- 
dons take  in  each  case?  How  long  do  they  endure, 
and  what  is  their  fate  ?  Make  drawings  illustrating 
the  points  made. 

The  development  of  the  leaves  also  offers  a  point 
of  interest.  Make  drawings  of  the  first,  second, 
and  third  leaves  of  the  bean,  and  note  the  differ- 
ence in  their  structure.  Make  drawings  and  note 
form  of  the  five  leaves  which  appear  first  on  the 
stem  of  the  pea.     It  will  be  seen  in  both  instances 


180  THE  NATURE  AND    WORK  OF  PLANTS 

that  the  first  leaf  that  appears  is  simple,  the  blade 
not  being  divided  or  branched.  In  the  bean  it  is 
an  active  green  leaf,  but  in  the  pea  it  is  a  small 
three-pointed  scale  or  bract  which  is  not  very 
conspicuous  and  may  be  easily  overlooked.  The 
second  leaf  will  show  greatest  difference  from  the 
first  in  the  bean,  and  the  third  of  that  plant  will 
be  very  nearly  the  form  seen  on  the  adult  stems. 
The  second  leaf  of  the  pea,  however,  is  but  little 
more  developed  than  the  first,  but  the  third,  fourth, 
and  fifth  show  increased  development.  Perhaps  not 
until  the  sixth  or  seventh  leaf  is  reached  will  you 
find  the  characteristic  leaf  of  the  pea.  The  incom- 
plete or  simple  leaves  of  seedlings  are  termed  em- 
bryonic leaves,  and  it  is  a  theory  of  the  botanist 
that  they  represent  forms  used  by  the  species  in 
earlier  stages  of  its  history,  and  these  leaves  are 
the  leaves  of  its  ancestors,  slightly  changed  of 
course.  Thus  many  thousands  or  millions  of  years 
ago  the  group  of  plants  from  which  beans  have 
sprung  were  furnished  with  simple  leaves  like  those 
shown  just  above  the  cotyledon.  Later  these  plants 
began  to  form  lobes  in  the  lamina,  and  finally  it 
was  branched  or  divided  as  in  the  modern  bean. 
There   may  be   still  other  stages  between  these,  or 


SEEDS  AND  FRUITS  181 

before  any  of  them,  which  are  lost.  For  while  the 
plant  may  repeat  a  part  of  its  ancient  history,  we 
cannot  be  quite  sure  that  it  has  recounted  all  of 
it.  In  fact,  it  would  be  almost  impossible  for  it  to 
do  so.  In  the  instance  of  the  pea,  the  bracts  or 
first  leaves  may  be  simply  the  bases  of  incomj^lete 
organs  and  may  not  represent  the  lamina  at  all. 


IX.     THE   POWER   OR   ENERGY   OF   THE 
PLANT 

218.  Enercjij  in  the  jjlant.  —  In  the  preceding 
paragraphs  the  plant  has  been  shown  to  do  a  great 
many  kinds  of  work,  and  to  use  great  force  or 
power  in  carrying  out  these  processes.  The  push- 
ing of  roots  through  the  soil,  the  movements  of 
these  and  other  organs,  the  lifting  of  the  food  from 
the  soil  to  the  top  of  the  stems,  the  pumping  of 
the  water  from  the  roots  to  the  leaves,  —  a  distance 
which  may  be  as  great  as  five  hundred  feet,  —  are 
examples  of  external  forms  of  work  done  by  the 
plant.  The  living  plant  is  only  a  machine,  and  it 
cannot  originate  or  give  rise  to  energy  any  more 
than  a  steam  engine  may.  The  engine  is  simply 
a  device  for  using  the  energy  released  when  fuel 
is  burned  in  its  furnaces.  This  energy  in  the  form 
of  heat  converts  water  into  steam,  and  it  may  be 
conducted  through  pipes  and  made  to  act  in  a  man- 
ner convenient  to  the  operator. 

219.  Sources  of  energy.  —  The  plant  receives  en- 
ergy   from   sunlight,   and    from    the   chemical  com- 

182 


THE  POWER    OR   ENERGY  OF  THE  PLANT         183 

pounds  which  it  absorbs  from  the  soil,  and  also 
makes  use  of  the  physical  energy  exhibited  by  cer- 
tain substances. 

220.  Sunlight  as  a  source  of  energy.  —  The  por- 
tion of  sunlight  absorbed  by  leaves  is  used  as  a 
means  of  separating  compounds  in  such  manner 
that  the  parts  of  these  compounds  will  form  new 
and  more  powerful  unions.  It  is  as  if  one  had  two 
magnets,  to  each  of  which  was  adhering  a  small  bar 
of  iron.  By  the  use  of  a  small  amount  of  force 
the  magnets  and  the  iron  may  be  separated,  and 
then  the  magnets  will  mutually  attract  each  other 
with  greater  force.  Sunlight  tears  away  some  of 
the  oxygen  united  with  the  magnet  hydrogen  to 
form  water,  and  some  of  the  oxygen  united  with 
the  magnet  carbon  in  carbon  dioxide,  leaving  the 
carbon  and  hydrogen  to  rush  together,  forming  a 
stronger  chemical  union  and  carrying  with  them 
a  portion  of  the  oxygen. 

221.  Chemical  compounds  as  a  source  of  energy. — • 
Animals  get  all  their  energy  from  chemical  com- 
pounds used  as  food.  The  foods  of  the  plant  are 
very  simple  compounds,  but  they  gain  some  energy 
in  this  manner. 


184  THE  NATURE  AND   WORE  OF  PLANTS 

222.  Physical  attraction  as  a  source  of  energy. 
—  Compounds  often  exert  an  attraction  for  each 
other,  and  the  resulting  union  does  not  change  the 
composition  of  either  of  them.  Thus  sugar  and 
salt  attract  water,  and  will  even  draw  it  from  the 
air;  but  when  sugar  and  water  come  together,  they 
form  a  solution,  and  the  composition  of  neither  is 
disturbed.  The  water  may  be  driven  off  and  the 
sugar  will  remain  as  before.  Examples  of  this 
were  seen  in  the  experiments  illustrating  the  action 
of  the  root-hair. 

223.  Release  of  energy.  —  After  energy  has  been 
acquired  by  the  plant,  it  may  be  transformed  or 
released  and  made  to  do  various  kinds  of  work. 
The  principal  method  of  releasing  energy  is  the 
same  as  that  used  in  the  steam  engine,  and  con- 
sists in  oxidizing  or  huming  the  compounds  which 
contain  it. 

224.  Respiration  or  hreathing.  —  The  slow  burn- 
ing of  material  goes  on  almost  constantly  in  all 
living  substance,  and  it  is  essentially  the  same  kind 
of  a  process  in  both  plants  and  animals.  It  is  most 
rapid  in  growing  tissues  and  slowest  in  resting  seeds 
and  spores.     It  is  still  maintained,  however,   and  it 


THE  POWER   OR  ENERGY  OF  THE  PLANT         185 

is  this  slow  burning  up  of  the  protoplasm  which  is 
responsible  for  the  death  of  old  seeds.  At  extremely 
low  temperatures  it  ceases,  as  do  all  the  activities 
of  protoplasm.  Thus  when  seeds  are  placed  in 
liquid  air  at  a  temperature  of  nearly  three  hundred 
degrees  below  zero,  Fahrenheit,  it  can  be  stated 
with  certainty  that  breathing  as  well  as  all  other 
activities  have  ceased. 

225.  Changes  in  the  air  j^'i^oduced  by  breathing.  — 
The  oxygen  used  in  breathing  is  sometimes  taken 
from  compounds  in  the  plant,  and  then  the  burn= 
ing  is  sometimes  incomplete,  and  no  external  evi- 
dence of  it  can  be  seen.  In  one  form,  however, 
marked  changes  are  made  in  the  air.  This  may  be 
detected  by  the  following  experiment.  Secure  three 
fruit  jars  and  fill  one  half-full  of  peas  which  have 
been  soaked  in  water  for  a  day,  put  the  same 
quantity  of  dried  peas  in  the  second,  and  allow 
the  third  to  remain  empty.  Cover  tightly.  A  day 
later  prepare  a  small  torch  by  fastening  a  section  of 
a  candle  an  inch  long  to  a  piece  of  wire  a  foot  long. 
A  bit  of  string  soaked  in  oil  will  answer  equally 
well.  Light  the  torch,  remove  the  cover  of  the 
empty  jar,  and  lower  the  blaze  into  it.     The  flame 


186  THE  NATUBE  AND    WORK  OF  PLANTS 

remains  unchanged.  Repeat  with  the  jar  of  dried 
seeds.  No  effect  is  noticeable.  Repeat  with  the  ger- 
minating seeds.  The  blaze  is  extinguished.  Relight 
and  test  again.  The  extinguishment  of  the  blaze  has 
a  double  meaning.  The  oxygen  of  the  air,  which 
is  necessary  to  support  the  blaze,  has  been  used  by 
the  germinating  seeds  for  their  burning.  In  its 
place  is  the  carbon  dioxide  which  has  been  produced, 
which  now  forms  one-fifth  of  the  air  in  the  jar. 

The  burning  of  the  quiescent  dry  seeds  is  so  slow 
that  it  has  not  produced  any  change  in  the  ah"  about 
them.  The  second  and  third  jars  show  that  it  is  not 
the  influence  of  the  jar  which  extinguishes  the  blaze. 

The  above  experiment  may  be  performed  with 
mushrooms,  flowers,  or  any  portion  of  the  living 
plant  which  does  not  contain  chlorophyl.  Breath- 
ing is  carried  on  by  all  parts  of  the  plant,  but  the 
portions  which  contain  chlorophyl  take  up  the  car- 
bon dioxide  thirty  times  faster  than  it  is  formed  by 
the  same  organ.  Thus,  if  green  plants  were  enclosed 
in  the  jar  the  carbon  dioxide  would  be  quickly  used, 
and  the  amount  of  oxygen  increased. 

226.  Plants  by  day  and  hy  night.  —  During  the 
daytime  the  green  plant  takes  up  thirty  times  as 


THE  POWER   OR   ENERGY  OF  THE  PLANT         187 

much  carbon  dioxide  as  it  gives  off,  and  throws  off 
thirty  times  as  much  oxygen  as  it  uses.  At  night, 
however,  it  burns  and  exhibits  only  the  action  of 
the  germinating  seeds.  This  has  led  to  a  popular 
belief  that  living  plants  in  a  sleeping  room  have  an 
unhealthful  effect  on  the  occupant  because  of  the 
carbon  dioxide  which  they  throw  off.  Such  effects 
are  largely  imaginary,  because  all  the  plants  which 
could  be  crowded  into  a  bedroom  would  not  give 
off  as  much  carbon  dioxide  as  a  single  candle. 

227.  Relation  of  the  living  world  and  the  atmos- 
phere. —  It  is  also  a  common  impression  that  the 
activities  of  plants  and  animals  balance  each  other 
in  maintaining  the  composition  of  the  atmosphere, 
and  it  will  be  profitable  to  recall  some  of  the 
general  facts  bearing  upon  this  question. 

A  single  person  throws  about  two  pounds  of 
carbon  dioxide  into  the  atmosphere  daily,  and  the 
total  product  of  the  human  race  for  twenty-four 
hours  is  twenty-seven  or  twenty-eight  hundred  mill- 
ion pounds.  The  breathing  of  the  lower  animals  and 
plants  and  the  products  of  fires  bring  the  total 
amount  of  carbon  dioxide  produced  daily  by  living 
beings  directly  and  indirectly  to  about  six  thousand 


188  TEE  NATURE  AND    WORK  OF  PLANTS 

million  pounds.  Fifty  square  yards  of  leaf  surface 
will  take  up  as  much  carbon  dioxide  as  may  be 
thrown  off  by  a  single  person,  and  furnish  as  much 
oxygen  as  he  would  need.  When  the  immense  area 
of  the  leaves  of  all  the  plants  in  the  world  is  con- 
sidered, it  is  found  at  the  extremest  low  estimate 
that  the  vegetable  world  uses  more  than  twice  as 
much  carbon  dioxide  as  may  be  produced  by  living 
agencies,  and  gives  off  twice  as  much  oxygen  as 
they  consume.  No  appreciable  change  has  ever 
been  found  in  the  composition  of  the  atmosphere 
with  respect  to  these  gases,  however,  and  it  must 
be  concluded  that  other  agencies  are  at  work  which 
use  these  gases ;  otherwise  the  air  would  be  grow- 
ing poorer  in  carbon  dioxide  and  richer  in  oxygen. 
It  is  found  that  changes  are  constantly  going  on 
in  the  soil  and  in  the  rocks,  which  liberate  and 
take  up  these  gases  in  quantities  which  make  the 
amounts  used  by  living  things  seem  very  insignificant, 
and  that  the  waters  of  the  sea  form  a  vast  store- 
house for  them.  Then  again  the  atmosphere  con- 
tains about  eight  thousand  billions  of  pounds  of 
carbon  dioxide,  and  if  the  activities  of  plants  were 
to  cease  entirely,  it  would  be  many  hundreds  of 
years    before    the    proportion    of    gases    would    be 


THE  POWER   OB  ENERGY  OF  THE   PLANT         189 

altered  sufficiently  to  be  sensible  to  any  other  living 
thing. 

Furthermore,  plants  are  capable  of  using  nearly 
two  hundred  times  as  much  carbon  dioxide  as  they 
now  get  in  the  atmosphere,  so  that  there  is  no 
actual  balance  between  plants  and  animals  so  far 
as  the  atmosphere  is  concerned. 

228.  Energy  of  ^j/iT/s/caZ  attraction.  —  It  has 
been  seen  that  the  attraction  of  sugar  for  water 
results  in  pulling  water  into  the  plant  containing 
food.  It  is  also  known  that  this  same  action  car- 
ries fluids  from  one  part  of  the  body  to  another, 
and  serves  especially  in  aiding  to  carry  the  current 
of  water  from  the  roots  to  the  leaves.  It  is  this 
power  of  attraction  of  one  substance  for  another 
which  fills  the  cells  with  water,  making  them  tense 
and  firm.  The  firmness  of  the  cells  filled  with 
water  in  this  manner  is  all  that  holds  up  the  soft 
stems  of  herbaceous  plants.  When  the  water  is 
driven  off  by  heat  this  work  is  no  longer  accom- 
plished, and  the  stems  wilt  and  fall  over.  Water 
is  attracted  into  the  cells  by  certain  substances,  and 
if  substances  with  stronger  attractive  power  are 
placed  outside  the  plant,  the   water  will   be  with- 


190  THE  NATURE  AND    WORK  OF  PLANTS 

drawn  from  the  cells,  and  the  plant  will  become  as 
limp  as  if  it  were  wilted  in  the  sun.  Cut  off  the 
plump,  rapidly  growing  shoots  of  any  soft-bodied 
plant  and  lay  them  in  a  deep  dish  which  contains 
water  saturated  with  sugar  or  salt.  Examine  after 
a  few  hours.  The  shoots  will  be  found  limp  and 
weak,  and  bend  over  when  you  attempt  to  hold 
them  upright  by  the  basal  parts  of  the  stems. 

229.  Outward  loork  acco7n2)lished  hy  ^;/i?/s/crtZ 
attraction.  —  When  water  is  attracted  into  a  cell 
the  cell  expands  with  a  force  which  may  be  equal 
to  twenty  times  the  pressure  of  the  atmosphere. 
The  expansion  of  the  cells  of  a  root  will  split 
apart  rocks  and  perform  similar  work.  This  may 
be  demonstrated  as  follows:  Fill  a  narrow-necked 
bottle  of  a  capacity  of  four  to  eight  ounces  with 
dried  peas.  Next  pour  in  as  much  water  as  the 
bottle  will  hold,  and  then,  without  admitting  air, 
invert  the  bottle,  and  set  the  mouth  in  a  dish  of 
water.  Examine  a  day  or  two  later.  The  cells  of 
the  seeds  will  have  taken  in  so  much  water  under 
the  attractive  power  of  the  substances  which  they 
contain  that  they  have  expanded  and  burst  the 
walls  of  the  bottle. 


X.   RELATIONS   OF   PLANTS   TO   EACH 
OTHER  AND   THEIR  HABITAT 

230.  Societies  and  communities.  —  All  living  things 
exist  in  the  form  of  societies  and  communities,  in 
a  manner  which  is  fairly  well  illustrated  by  the 
mode  of  life  of  the  human  family.  Men  attempt 
to  live  in  the  places  where  they  may  most  easily 
obtain  food,  clothing,  and  shelter,  and  enjoy  comfort. 
Nearly  every  man  devotes  his  energy  to  certain 
kinds  of  work,  and  lives  in  a  suitable  house  so  far 
as  possible  for  him  to  do  so.  It  may  be  readily  seen 
that  the  men  devoted  to  one  trade  could  not  form  a 
community.  Thus  the  tailors,  tinners,  blacksmiths, 
carpenters,  and  merchants  could  not  separately  form 
communities,  for  a  community  is  made  up  of  repre- 
sentatives of  each  of  these  and  many  other  kinds  of 
workers.  A  community  comprises  the  people  in  a 
town,  village,  city,  or  a  region  of  the  country  occu- 
pied by  a  village  and  outlying  land,  according  to 
the  habits  of  the  people.  Generally  some  one  trade 
or  group  of  workers  occupies  the  most  prominent 
place  in  the  community,   and  this  causes   it  to  be 

191 


192  THE  NATURE  AND    WORE  OF  PLANTS 

spoken  of  as  a  farming  community,  a  mining  camp 
or  town,  a  manufacturing  town  or  city,  a  fishing 
village  or  shipping  town,  according  to  the  kind  of 
work  most  prominent  in  its  affairs. 

231.  Plant  societies.  —  The  plants  of  different 
areas  on  the  earth's  surface  are  unlike  in  general 
form,  are  made  up  of  different  species,  and  secure 
the  things  essential  to  life  in  very  different  manners, 
and  constitute  a  comrriunity.  The  principal  commu- 
nities in  northern  United  States  are  forests,  mead- 
ows, sivamj:)  societies,  j^otid  societies,  heach  marshes, 
thickets,  heaths,  moors,  sand,  and  rock  societies,  beside 
many  others  of  more  or  less  frequent  occurrence. 
The  general  aspect  of  a  society  in  the  landscape  is 
determined  by  its  largest  or  most  prominent  member. 
Thus,  for  instance,  if  the  chief  member  is  a  tree,  the 
community  will  be  a  forest.  Further,  the  forest  goes 
by  the  name  of  the  most  abundant  tree,  and  there 
are  oak  forests,  beech,  maple,  and  pine  forests  or 
communities.  In  many  cases  communities  have 
taken  on  the  names  of  the  place  in  which  they  live, 
as  in  swamp,  rock,  beach,  and  sand  societies. 

232.  Foundations  of  society.  —  The  things  which 
determine   the    character   of   any  plant  community 


RELATIONS   OF  PLANTS    TO  EACH  OTHER         193 

are,  —  the  water  siqjplij,  tem^yerature  of  the  soil  and  air, 
jihysical  and  chemical  jjrojjer^ties  of  the  soil,  winds, 
and  light.  The  length  of  time  during  which  these 
conditions  have  continued  unchanged  in  any  given 
piece  of  land  or  country  is  also  a  very  important 
factor. 

233.  Communities  change.  —  Communities  are  al- 
ways in  a  state  of  being  changed,  and  they  may 
disappear  from  any  place  and  others  may  replace 
them.  A  good  example  of  this  will  be  seen  if  a 
marsh  or  pond  is  drained.  During  the  existence  of 
the  pond,  water  societies  only  could  live  there.  The 
mud  left  by  the  pond  will  allow  societies  of  lower 
plants  to  form  a  green  coating  over  its  surface. 
After  a  time  liverworts,  mosses,  and  ferns  may  find 
suita-ble  conditions  here.  Later,  when  the  mud  has 
dried  and  the  soil  becomes  loose  and  loamy,  llowering 
plants  will  find  a  foothold,  and  if  imdisturbed,  young 
trees  may  grow  up,  and  thus  the  place  once  occupied 
by  a  pond  society  will  be  the  residence  of  a  forest. 
But  even  then  the  changes  are  not  all  past.  The 
action  of  the  first  kind  of  trees  on  the  soil  may  fit 
it  for  the  growth  of  other  trees,  and  the  first  forest 
may  be  replaced  by  a  different  one.     Similar  move- 


194  THE  NATURE  AND    WORK  OF  PLANTS 

merits  have  been  followed  in  the  development  of 
humcan  societies.  The  hunter  and  the  pioneer  first 
occupy  the  soil  or  land,  to  be  followed  by  the  miner 
and  the  farmer,  and  then  by  the  manufacturing  town 
or  the  city. 

234.  Water  and  ^9?aw^s.  —  The  plant  is  ex- 
tremely sensitive  about  its  supply  of  water.  Not 
only  must  it  have  a  certain  amount  of  rainfall  each 
year,  but  the  rain  must  be  given  throughout  the 
whole  year,  instead  of  all  at  one  time.  The  amount 
capable  of  being  retained  by  the  soil  and  the  salts 
it  contains  are  also  of  importance.  The  pond  socie- 
ties float  in  or  on  top  of  the  water,  or  are  submerged 
beneath  it. 

235.  Temperature  and  plants.  —  Each  species 
requires  a  certain  number  of  warm  days  for  its 
development  and  can  endure  only  certain  low  tem- 
peratures. Thus  our  summers  in  the  Middle  states 
are  warm  enough  for  the  castor-oil  plant  out  of  doors, 
but  the  low  temperatures  of  winter  kill  it.  The 
warmth-retaining  value  of  the  soil  is  to  be  taken 
into  account  in  this  connection.  The  surface  of  the 
country  is  also  a  feature.  In  broken  hilly  regions 
the  cold   air  settles   down   in   the  valleys,  making 


RELATIONS   OF  PLANTS   TO  EACH  OTHER         195 

them  much  colder  than  the  near-by  hill-tops,  and 
these  valleys  are  much  warmer  in  the  daytime  than 
the  hills. 

236.  TJie  soil  and  plants.  —  The  chemical  char- 
acter of  the  soil  with  respect  to  the  kind  and 
amount  of  food  it  contains,  and  its  physical  qualities 
due  to  its  coarseness  or  fineness,  and  jDower  to  hold 
water,  as  well  as  its  heating  properties,  influence 
the  communities  growing  upon  it.  The  principal 
soils  are  rock,  sand,  lime,  humus  or  loam,  and  clay. 
Beside  the  soil  itself,  the  coverings  of  snow,  leaves, 
or  living  2^lants  are  of  value  to  the  community. 

237.  Light  and  ^9/a?i/Js.  —  Light  is  necessary  for 
all  green  plants,  but  some  are  able  to  make  use  of 
rays  of  less  intensity  than  others,  and  have  altered 
the  structure  of  their  entire  bodies  to  suit  this  adapta- 
tion. The  species  which  can  use  the  weaker  light 
usually  stand  under  those  that  require  the  full  blaze 
of  the  sun,  in  the  shadow  of  rocks,  on  northern 
slopes,  or  if  they  are  aquatic  species  they  live  at 
some  depth  under  the  surface  of  the  water.  Along 
a  sea  beach  the  area  between  high  and  low  water 
which  is  thus  exposed  to  the  full  force  of  tlie  suu 
part  of  every  day  is  inhabited  by  green,  brown,  and 


196  THE  NATURE  AND    WORK  OF  PLANTS 

red  seaweeds.  The  top  layer  of  water  extending  to 
a  depth  of  a  hundred  and  fifty  feet  is  inhabited  by 
red  and  some  brown  algae,  and  below  this  depth  for 
a  short  distance  the  red  algge  alone  find  suitable 
conditions.  Bacteria  may  live  at  depths  of  over  half 
a  mile  or  in  complete  darkness,  in  the  same  manner 
that  mushrooms  or  other  non-green  species  may  live 
in  caves  completely  shut  off  from  the  light. 

238.  Wind  and  plants.  —  The  wind  affects  the 
character  of  the  stems  developed,  and  is  a  very  im- 
portant factor  in  carrying  pollen  from  one  flower  to 
another,  disseminating  seeds,  spores,  and  other  repro- 
ductive bodies.  Its  general  direction  is  an  important 
factor  in  determining;  the  rainfall  also. 

239.  Forests.  —  The  best  idea  of  a  community 
may  be  gained  from  the  study  of  one  as  it  lives  in  an 
undisturbed  condition,  and  it  will  be  most  profitable 
to  make  the  first  observations  on  the  subject  in  a 
forest,  since  the  relations  of  its  members  are  more 
easily  determined  than  m  some  others. 

In  order  that  the  work  upon  this  point  should 
have  any  great  value  it  should  be  extended  through- 
out the  greater  part  of  a  season,  though  many  fea- 
tures of  interest  may  be  made  out  in  a  single  visit. 


RELATIONS  OF  PLANTS   TO  EACH  OTHER        197 

It  will  be  found  most  convenient  to  select  the  most 
accessible  forest  and  make  visits  of  several  hours 
each  to  it  on  several  days,  which  may  be  a  week  or 
a  month  apart.  This  may  be  done  by  using  the 
weekly  holiday  for  excursions,  which  may  also  be 
made  the  opportunity  of  collecting  material  for  other 
experiments,  and  for  the  observation  of  reproduction, 
dissemination  of  seeds  and  iruits,  action  of  leaves, 
etc.  It  is  indispensable  that  some  member  of  the 
party  should  be  able  to  identify  the  common  species 
of  plants  found  in  the  community,  and  it  will  be 
highly  profitable  and  necessary  that  all  should  use  a 
manual  in  taking  the  census  of  the  flora. 

On  the  first  visit  to  the  forest  walk  over  its  entire 
area,  or  enough  of  it  to  gain  a  general  idea  of  its 
extent,  the  character  of  its  surface,  whether  level  or 
hilly,  the  direction  in  which  it  slopes,  the  drainage, 
streams,  ponds,  or  lakes.  It  will  be  important  to  as- 
certain whether  the  forest  has  been  visited  by  fire  or 
damaged  by  grazing  animals.  Furthermore,  notes 
should  be  begun  and  carried  throughout  the  observa- 
tions upon  the  animals  which  inhabit  or  frequent  the 
forest,  and  their  influence  upon  the  distribution  of 
seeds  or  pollen. 

Is  the  soil  swampy,  moist,  or  dry  ?     What  is  its 


198  THE  NATURE  AND    WORK  OF  PLANTS 

composition  ?  Is  it  chiefly  sand,  clay,  or  rock  ?  Is 
the  rock  limestone,  granite,  or  quartz  ?  Is  the  soil 
covered  with  a  layer  of  fallen  leaves,  or  has  this  been 
destroyed  ? 

It  will  next  be  of  importance  to  determine  the 
trees  which  make  up  the  larger  members  of  the  com- 
munity. With  regard  to  this  point  two  kinds  may  be 
distinguished :  pure  and  mixed  forests.  A  pure  forest 
shows  but  one  kind  and  a  mixed  forest  many  kinds 
of  trees.  What  species  is  most  abundant  ?  Are  the 
trees  closely  crowded  together  so  as  to  completely 
shade  the  ground,  or  are  they  wide  apart,  thus  per- 
mitting light  to  reach  the  ground  and  the  growth  of 
many  other  plants  ?  Pure  forests,  made  up  of  pines, 
hemlocks,  or  beeches  generally  shade  the  ground  so 
completely  as  to  make  it  impossible  for  undershrubs 
to  live.  Oak,  maple,  and  hickory  forests  are  generally 
open  and  have  much  underbrush.  Make  a  map  of  the 
forest,  showing  the  facts  in  regard  to  the  occurrence 
of  the  different  kinds  of  trees.  The  trees  may  be 
evergreen,  retaining  the  leaves  throughout  the  winter, 
or  these  may  be  cast  in  the  autumn. 

Find  the  seedlings  or  young  specimens  of  the  trees, 
and  note  whether  they  have  found  a  foothold  in 
shaded  or  suuny  places.     Find  a  place  where  a  tree 


RELATIONS   OF  PLANTS   TO  EACH  OTHER         199 

or  cluiiip  of  trees  has  been  destroyed  or  died,  and 
note  whether  the  young  trees  which  are  springing 
up  in  their  places  are  of  the  same  species  as  the  dead 
ones.  This  will  do  much  to  indicate  the  ultimate 
fate  of  the  forest.  If  you  find  that  the  dead  trees 
are  being  replaced  by  the  same  kind,  it  would  mean 
that  the  condition  of  the  forest  would  remain  un- 
changed; but  if  different  ones  are  gaining  a  foothold 
the  entire  character  of  the  forest  would  be  changed 
in  the  course  of  time.  If  all  of  the  dead  trees  are 
replaced  by  a  single  species,  it  would  indicate  that 
finally  a  pure  forest  of  that  species  would  occupy  the 
locality  if  undisturbed  by  man. 

Find  the  seeds  and  fruits  of  the  trees  and  deter- 
mine the  manner  in  which  they  are  disseminated, 
and  their  endurance  of  cold  and  drought. 

If  possible  find  isolated  trees,  and  note  the  dis- 
tance to  which  their  seeds  have  been  carried. 

Do  they  germinate  as  soon  as  set  free  from  the 
parent,  or  do  they  lie  quiescent  until  the  following 
season?     Observe  the  manner  of  germination. 

Traverse  the  entire  margin  of  the  forest,  and 
note  whether  it  is  spreading  or  not.  Do  you  find 
young  seedlings  outside  the  area  occupied  by  the 
taller  trees? 


200  THE  NATURE  AND    WORK  OF  PLANTS 

Note  the  occurrence  of  shrubs  and  small  hushes. 
Are  they  found  under  trees  or  in  openmgs  or  mar- 
gins ?  In  an  open  or  mixed  forest  there  may  be 
a  continuous  layer  of  shrubs  over  the  entire  area, 
while  in  close  woods  they  can  find  suitable  con- 
ditions only  in  the  openings.  Plot  the  positions 
of  the  shrubs  and  determine  the  species  repre- 
sented. 

Climbers  will  be  found  in  greater  or  less  abun- 
dance. Some  of  these  will  be  attached  to  the 
trunks  of  the  tallest  trees,'  while  others  are  sup- 
ported by  the  shrubs  and  low  bushes. 

The  carjjet,  or  layer  of  plants  which  cling  to 
the  surface  or  rise  only  a  short  distance  above  it, 
will  vary  greatly  with  the  manner  in  which  the 
trees  are  associated.  In  close  pure  forests,  like 
the  hemlock,  the  carpet  will  be  sparse  and  almost 
entirely  lacking  from  the  depths  of  the  wooded 
area.  A  few  low-growing  species  may  be  found 
in  open  places  or  clinging  to  exposed  rocks  or 
hillocks.  In  this  carpet  will  be  found  mosses, 
ferns,  liverworts,  creeping  and  trailing  vines  and 
shrubs,  and  herbaceous  plants  which  form  tufts  or 
rosettes  of  leaves  which  lie  close  to  the  surface, 
like   the   sedges,   some    grasses,   or    the   saxifrages. 


RELATIONS   OF  PLANTS   TO  EACH  OTHER        201 

The  loose  soil  is  inhabited  by  scores  of  species  of 
fungi,  which  send  their  long  strands  in  every  direc- 
tion, and  occasionally  develop  the  sporophyte  in 
the  form  of  stalked  capsules,  puff-balls,  or  um- 
brella-shaped "toadstools"  or  "mushrooms,"  while 
the  soil  is  teeming  with  bacteria,  which  cause  the 
decay  of  the  leaves.  It  would  be  most  interest- 
ing to  compare  the  carpet  of  a  swampy  portion 
of  the  forest  with  that  of  a  slope  or  wooded   hill. 

240.  Relations  of  members  of  the  forest.  —  The 
relations  of  the  members  of  the  forest  are  most 
close  and  intimate.  A  disturbance  of  one  is  likely 
to  influence  all  the  others.  Thus  the  leaves  and 
twigs  from  the  trees  form  a  light  layer  of  loose  soil 
or  humus  necessary  for  the  growth  of  mosses  and 
ferns,  and  the  freshly  fallen  layer  covers  over  the 
members  of  the  carpet  each  autumn  with  a  blanket 
which  protects  them  from  the  extremes  of  the  winter. 
On  the  other  hand,  the  destruction  of  the  forest  and 
the  loose  soil  by  fire,  or  the  action  of  grazing  animals, 
would  result  in  injuries  to  the  trees. 

241.  Time  of  blooming.  —  It  needs  but  the  most 
casual  acquaintance  with  plants  to  know  that  they  do 
not  all  bloom  and  ripen  seeds  at  the  same  time  of  the 


202  THE  NATURE  AND   WORK  OF  PLANTS 

year.  And  it  may  be  recalled  that  after  the  opening 
of  the  growing  season  in  spring  there  is  a  constant 
succession  of  flowers  throughout  the  summer.  This 
is  not  an  accidental  occurrence.  Each  species  tends 
to  bloom  and  mature  its  seeds  at  a  time  when  it  may 
do  so  to  the  best  advantage  and  with  the  least  com- 
petition. Without  going  into  all  the  points  involved, 
it  is  to  be  seen  that  if  all  the  plants  which  need 
insects  to  carry  their  pollen  were  to  bloom  at  the 
same  time,  the  supply  of  honey  they  offer  could  not 
secure  the  attention  of  the  insects  to  more  than 
a  few  individuals  of  each  species.  As  it  is,  how- 
ever, every  species  secures  a  share  of  work  of  the 
insects  in  cross-pollination,  since  only  a  few  species 
offer  honey  at  the  same  time,  and  the  seeds  are 
also  disseminated  with  less  competition.  If  all 
the  crops  of  a  farmer  were  to  be  harvested  at 
the  same  time,  they  could  neither  be  cared  for  nor 
shipped  properly. 

242.  Seasonal  activiUj.  —  It  must  not  be  sup- 
posed that  the  activity  of  the  members  of  the  forest 
community  is  confined  to  the  season  in  which  flowers 
appear.  If  a  close  examination  of  the  community 
is  made  in  February  or  March,  it  will  be  found  that 


RELATIONS    OF  PLANTS    TO   EACH  OTUER         203 

many  of  the  mosses  have  developed  the  sporophytes 
with  their  conspicuous  capsules  while  the  soil  is  still 
frozen.  The  closely  lying  rosettes  and  evergreen 
leaves  have  taken  advantage  of  every  sunny  day, 
and  the  flowering  shoots  will  spring  up  into  the  air 
on  the  earliest  approach  of  spring.  One  species,  a 
shrub,  the  witch-hazel,  blooms  after  its  leaves  have 
fallen  in  October  and  November,  and  ripens  its  seeds 
the  next  summer.  Make  note  of  the  species  of 
all  parts  of  the  forest  which  bloom  in  the  early 
part  of  the  spring,  during  a  period  of  a  month. 
Some  kinds  will  be  found  which  form  flowers  be- 
fore the  leaves  are  up  out  of  the  ground,  or  are 
unfolded  from  the  buds.  The  first  period  should 
cover  all  the  time  until  the  leaves  of  the  trees 
have  appeared. 

Make  similar  note  of  the  species  which  bloom 
before  the  opening  of  summer,  or  June  1st.  What 
are  the  earliest  species  to  mature  seeds  and  drop 
them  to  the  ground  ?  Do  these  seeds  germinate  at 
once,  or  lie  dormant  until  the  next  year? 

Keep  one  or  two  species  under  constant  observa- 
tion, and  determine  the  length  of  time  between  the 
beginning  of  growth  and  the  maturation  of  the 
seeds  and  their  germination. 


204  THE  NATURE  AND    WORK  OF  PLANTS 

It  will  be  of  equally  great  interest  to  follow  the 
activities  of  the  forest  members  through  early  sum- 
mer, midsummer,  late  summer,  autumn,  and  late 
autumn,  until  the  closing  of  the  season. 

243.  Families  and  species  in  the  community. — 
The  work  outlined  in  the  previous  pages  should  en- 
able the  student  to  make  a  census  of  the  families 
and  species  which  make  up  the  community.  This 
should  be  done  in  connection  with  the  study  of 
the  various  elements  in  the  forest.  The  student 
should  provide  himself  with  a  manual  of  the  flora 
of  the  region  in  which  he  is  located,  and  make 
himself  familiar  with  the  use  of  it  so  that  he  can 
identify  the  majority  of  the  species  met  with.  The 
study  of  the  forest,  enables  one  to  group  plants  ac- 
cording to  habit  and  place  in  the  community,  but 
the  study  of  the  flora  gives  a  classification  accord- 
ing to  relationship  and  descent. 

Bring  together  specimens  of  species  belonging  to 
the  same  genus,  or  family,  and  note  their  differences 
and  similarities  in  appearance. 

Compare  individuals  of  the  same  species  w^hich 
live  in  different  kinds  of  soil,  or  in  more  or 
less   light.      If   possible,    compare   a   swamp   forest 


RELATIONS  OF  PLANTS   TO  EACH  OTHER        205 

with   an   upland   forest   in   all   the   above    particu- 
lars. 


244.  3feadoivs.  —  Natural  meadows  will  not  be 
easy  to  find  in  the  regions  accessible  to  most  readers 
of  this  book.  All  have  been  mowed,  or  pastured 
by  grazing  animals  to  such  extent  that  the  origi- 
nal arrangement  of  the  various  members  of  the 
community  has  been  very  much  disturbed.  Noth- 
ing makes  this  more  apparent  than  to  find  a 
meadow  that  has  been  allowed  to  run  to  weeds. 
This  does  not  mean  that  the  meadow  returns  to 
its  natural  state.  But,  as  soon  as  man  ceases  to 
protect  the  plants  he  wishes  to  cultivate  and  to  re- 
new them  by  additions  of  seed  brought  from  else- 
where, they  come  into  competition  with  vigorously 
growing  species  which  overtop  them  and  partially 
crowd  them  out,  resulting  in  a  new  meadow.  It 
may  be  seen  that  the  chief  members  in  a  meadow 
are  low  grasses,  clovers,  small  creepers,  a  few  stray 
mosses  and  liverworts,  and  a  large  number  of  peren- 
nial herbs  which  form  rosettes  of  leaves  on  the  sur- 
face and  send  up  tall  flowering  stalks,  like  the 
thistle,  ironweed,  mullein,  joe-pye,  and  many  others. 
Perhaps   the  most  natural  meadows  will  be  offered 


206  THE  NATURE  AND    WORK  OF  PLANTS 

by  the  open  spaces  in  woodlands.  Observe  a  spot 
of  this  character,  and  note  whether  the  young  trees 
from  the  forest  are  taking  possession  or  not. 

245.  Hock  societies.  —  Find  a  set  of  cliffs  or 
exposed  ridge  of  rocks,  and  note  the  character  of 
the  vegetation  that  finds  a  foothold  there.  It  will 
be  seen  that  the  distribution  of  the  rock  plants  is 
limited  quite  exactly  by  the  extent  of  the  stone  on 
which  they  grow.  This  is  perhaps  the  most  strik- 
ing feature  about  these  communities.  Forests  may 
cover  many  square  miles  in  extent,  but  rock  socie- 
ties usually  extend  over  a  few  square  yards  only. 
Still  another  feature  will  be  brought  out  in  a  com- 
parison of  the  rock  society  and  the  forest ;  the  thou- 
sands of  individuals  in  the  forest  crowd  each  other 
fiercely  for  space  in  which  to  live,  while  the  mem- 
bers of  the  rock  societies  are  scattered  about  over  the 
hard  surface,  finding  a  foothold  where  they  may  in 
any  convenient  crevice  or  roughened  area.  Observe 
a  rock  society  throughout  a  portion  of  the  season, 
and  make  a  census  of  its  members.  The  number  of 
seed  plants  will  be  small.  Ferns  will  probably  be 
represented,  the  mosses  will  form  clumps  or  coat- 
ings on  moist  portions  of  the  rock,  some  liverworts 


RELATIONS  OF  PLANTS   TO  EACH  OTHER        207 

will  be  present;  but  the  plant  most  at  home  in 
such  places  is  a  flat-crusted  one,  of  various  shades 
of  greenish-brown,  which  lies  flat  on  the  surface, 
growing  vigorously  in  the  wet  seasons,  and  shrink- 
ing to  a  hard  brittle  mass  in  dry  weather.  These 
are  the  lichens,  and  other  members  of  this  group 
sheathe  the  trunks  of  trees  in  the  forest.  Com- 
pare the  species  found  on  different  slopes  of  the 
rock. 

246.  Fond  societies.  —  Pond  societies  live  in  al- 
most all  waters  except  those  of  lakes  and  streams 
polluted  by  the  sewage  of  cities.  The  constitution 
of  such  societies  may  be  best  studied  in  a  pond,  lake, 
or  sluggish  stream,  and  a  boat  wdll  be  a  useful 
adjunct  for  the  exploration  of  depths  which  cannot 
be  reached  by  wading.  The  soil  above  high  water 
will  be  very  moist,  offering  suitable  conditions  for 
a  belt  of  cat-tails,  then  one  of  flowering  plants,  wil- 
lows, and  small  shrubs,  and  back  of  these  the  trees 
of  a  forest. 

On  the  first  visit  to  the  place  chosen  for  study, 
note  the  extreme  height  to  which  the  water  rises, 
and  examine  first  the  plants  growing  between  the 
high-water  mark  and  the  edge  of  the  water.    Identify 


208  THE  NATURE  AND   WORK  OF  PLANTS 

them,  and  note  their  habits  of  growth  and  repro- 
duction.    How  are  their  seeds  disseminated  ? 

Two  main  classes  of  plants  will  be  found  in  the 
water :  one,  which  anchors  to  the  bottom,  entirely 
submerged  or  partly  floating,  and  another  which 
floats  freely  on  the  surface.  In  the  first  class  will 
be  found  many  algae,  which  coat  the  stones  at  the 
bottom  of  the  shallow  places,  and  pond-weeds,  water- 
lilies,  arrow-leaf.  Determine  the  form  in  which 
these  species  live  through  the  winter.  Observe 
the  action  of  the  flower  stalk  of  the  water  arum. 
How  are  the  seeds  of  these  plants  spread  from  place 
to  place? 

One  of  the  members  of  this  group,  Vallisneria,  lives 
entirely  underneath  the  surface,  sending  its  pistillate 
flowers  up  to  the  surface,  at  the  end  of  long  stalks, 
while  those  containing  stamens  only,  break  off  and 
float.  After  the  pistils  have  received  the  pollen, 
the  maturing  seed-pods  are  drawn  down  under  the 
water  by  the  action  of  the  stalk,  which  assumes  the 
form  of  a  corkscrew.  Similar  action  is  exhibited  by 
the  water  hyacinth,  which  roots  in  the  mud  in 
shallow  water  or  floats  about  in  colonies.  When 
the  seeds  are  formed,  the  stalks  bend  over,  thrusting 
the  pods  under  the  water. 


RELATIONS   OF  PLANTS    TO   EACH  OTHER         209 

Note  the  species  floating  on  the  surface.  Among 
these  may  be  found  the  minute  duckweeds,  which 
look  like  small  leaves,  and  are  of  such  size  that 
several  of  them  may  be  laid  side  by  side  on  the 
thumb  nail.  The  leafiike  body  represents  both 
leaves  and  stems,  while  but  one  slender  root  is 
present  that  trails  down  in  the  water  and  serves  as 
a  keel  to  prevent  the  upsetting  of  the  leaf  (§31).  A 
vivid  coloring  may  be  seen  on  the  lower  side  of  these 
and  other  floating  aquatic  organs.  In  places  the  sur- 
face may  be  taken  up  by  numerous  specimens  of 
the  bladderwort  with  their  curiously  pouched  leaves 
full  of  minute  entrapped  animals.  In  quiet  pools, 
free  from  the  action  of  currents,  the  surface  will  be 
covered  by  heavy  masses  of  a  greenish  scum,  which 
has  a  greasy  feel  when  held  between  the  fingers. 
This  is  a  very  widely  distributed  alga,  Spirogyra, 
and  the  masses  are  composed  of  long  threads  made 
up  of  cylindrical  cells  placed  end  to  end.  What 
becomes  of  all  these  floating  members  of  the  com- 
munity in  the  winter  time  ?  How  do  they  reappear 
in  the  spring? 

247.  Locations  occiqned  by  members  of  different 
kinds    of  communities.  —  Low-lying    areas    may    be 


210  THE  NATURE  AND    WORK  OF  PLANTS 

found  in  land  which  is  not  well  drained  that  support 
groups  of  members  from  two  different  kinds  of  com- 
munities. This  is  to'  be  seen  in  places  covered  with 
water  by  the  spring  floods,  which  last  until  early 
summer.  During  this  time  the  only  species  living  in 
the  place  are  aquatic,  both  floating  and  rooting. 
With  the  advance  of  summer  the  water  evaporates, 
leaving  the  soil  dry  and  suitable  for  some  of  the 
rapidly  growing  members  of  swamp  or  meadow 
societies.  A  few  species  of  algae,  as  well  as  some 
of  the  seed  plants,  are  so  elastic  in  their  habits  that 
they  grow  under  both  conditions.  Thus  the  alga, 
green  velt  (Vaucheria),  may  float  or  rest  on  moist  soil 
with  equal  facility.  Species  which  cannot  adapt 
themselves  in  this  manner  live  through  the  unfavora- 
ble period  in  the  form  of  seeds,  tubers,  or  corms. 
The  continuation  of  either  the  floods  by  artificial  or 
natural  dams,  or  the  complete  drainage  of  the  area, 
will  result  in  the  extinction  of  the  members  of  the 
group  least  adapted  to  withstand  the  change. 

248.  Extermination  of  a  forest.  —  Find  a  piece  of 
woodland  from  which  the  trees  have  been  recently 
cut,  and  note  the  changes  ensuing  among  the  other 
members  of  the  community. 


RELATIONS   OF  PLANTS   TO  EACH   OTHER         211 

249.  Fields.  —  Examine  a  cultivated  field,  and 
note  the  kinds  or  species  which  exist  there  with  the 
crop  plants.  Do  they  belong  to  meadows,  forests, 
or  swamps  ? 

250.  Course  of  further  study.  —  The  work  followed 
in  this  book  will  give  a  general  idea  of  the  mode 
of  life  and  purposes  of  the  plant  world.  It  will 
next  be  in  order  for  the  student  to  examine  the 
structure  and  development  of  representative  types 
of  the  great  groups  in  which  plants  are  divided, 
—  algse,  fungi,  liverworts,  mosses,  ferns,  and  seed 
plants,  —  in  order  to  comprehend  their  descent  and 
relationship,  and  the  general  laws  by  which  plants 
adapt  their  bodies  to  their  environment. 


INDEX 


Absorbing  organ,  160,  163,  164. 
Absorption,    21,    24,    26,    60,    51, 
62. 

of  light,  63. 
Acer,  4,  5. 
Acids,  13,  18,  19. 
Adam  and  Eve,  130. 
Aerial  roots,  44. 
Air,  composition  of,  57. 

changes  in,  by  plants,  185,  186. 
Algfe,  14,  52,  53,  208,  209. 
Alkaloids,  19. 
Allium,  135. 
Amaranth,  59. 
Anchorage,  24. 
Annual  rings,  108,  113. 
Annuals,  113,  114. 
Antimony,  17. 

Apple,  67,  90,  117,  146,  175-178. 
Argon,  57. 
Arisaema,  27. 
Arrow-leaf,  208. 
Arsenic,  17. 
Ascent  of  sap,  104,  107. 
Ash,  10,  11,  15,  16. 
Assimilation,  21. 
Autumnal  colors,  67,  68. 
Autumnal  leaf  fall,  86. 
Axis,  main,  93. 

Bacteria,  37,  52,  53,  76,  137,  201. 

Ballast  roots,  30. 

Balsam  apple,  120. 

Bananas,  85. 

Bark,  110,  111. 

Bast.  98. 


Bean,  36,  39,  40,  49,  56,  75,  109, 

112,  148,  217. 
Beech,  4,  29,  96,  133. 
Beet,  19,  48,  69. 
Begonia,  54,  107,  132. 
Biennials,  113,  114. 
Birch,  67. 

Bladderwort,  66,  78,  79,  119,  209. 
Bleeding,  105. 
Bloom,  84. 
Bracts,  95. 

Breathing,  21,  184,  185. 
Bristles,  122,  172. 
Bromine,  16. 
Buds,  49,  66,  94,  115-119,  121,  132, 

133. 
Bulbs,  121,  133,  135. 
Bulbils,  133,  134,  135. 
Bulblets,  134-136. 

Cabbage,  84,  90. 
Cactus,  1,  123. 
Calcium,  16. 
Calcium  phosphate,  18. 
Calla,  27,  28,  102,  121. 
Canna,  70. 
Carbon,  16,  18,  61. 
Carbonic  acid,  37,  57,  61,  64,  IBS- 
IBS,  186,  187,  188,  189. 
Carrot,  11,  35. 
Castor-oil  plant,  194. 
Cat-tail,  207. 
Cellulose,  18. 
Charcoal,  10,  11. 
Cheat,  7. 
Cherry,  5,  133. 


213 


214 


INDEX 


Chess,  7. 

Chestnut,  95,  96,  101. 
Chlorine,  16,  18. 

Chlorophyl,  58,  59,  60,  61,  62,  63, 
64,  67,  69,  70,  76,  77,   144, 
183. 
Circular  movement,  112. 
Climbing  roots,  28. 
Clot-bur,  171-175. 
Clover,  41,  205. 
Club-mosses,  136. 
Cob,  166. 
Cockscomb,  159. 
Cocoanut,  155-162. 
Cocos  nucifera,  155-162. 
Cold,  influence  of,  89-92. 
Cold-air  drainage,  90. 
Coleus,  15,  69,  70,  90,  132. 
Collenchyma,  98. 
Colors,  58-71,  120. 
Columnar  roots,  29. 
Communities,  190-201. 
Compass  plants,  75,  76. 
Composition  of  plants,  8-11. 
Compounds  in  plants,  18. 

of  soil  30,  31. 

of  air,  57. 
Conacephalus,  51,  55,  136. 
Contact,  influence  upon  roots,  43. 

upon  tendrils,  126. 
Copper,  17. 
Corallorhiza,  48. 
Coral-root,  48,  77. 
Core,  176. 
Corn,  15,  99,  100,  111,  121,  155,  165- 

171. 
Corpse  plant,  47. 
Cotyledon,  160,  163,  164,  172,  173, 

179,  180. 
Cross-pollination,  202. 
Cuscuta,  45. 
Cuticle,  71,  84. 
Cuttings,  1,32,  133. 
Cystopteris,  136. 


Darwin,  43. 

Date,  162-165. 

Dew,  85,  106,  107. 

Dewberry,  137. 

Digestion,  77. 

Digestive  fluid,  79. 

Dissemination,    138,  149,  150,  151, 

170,  177. 
Distribution,  130.  g, 

Disuse,  effects  of,  48,  76,  77. 
Division,  136,  137. 
Dodder,  45-47. 
Duckweed,  30,  209, 

Egg,  132,  1.39,  149,  152,  153. 

Elements  in  plants,  16,  17. 

Elms,  4,  5,  41,  96. 

Embryo,  159,  160,  167,  172, 178,  179. 

Embryo  sac,  152,  153. 

Embryonic  tissue,  96,  108,  115,  116. 

Endosperm,  159,  167,  168. 

Endurance  of  seeds,  168-170. 

Energy  of  the  plant,  182-190. 

Euzym,  160,  168. 

Epidermis,  27,  156. 

Epsom  salts,  18. 

Equisetum,  13. 

Evergreens,  87. 

Extinction  of  species,  131. 

Families,  24. 

Ferns,  1,  4,  50,  80,  1,36,   139,   140, 

141,  145,  146,  193,  200. 
Fertilization,  151,  152. 
Ficus,  29. 

Fixation,  24-29,  50-53. 
Flower,  structure  of,  146-148. 
Food,  18. 

Food-formation,  57,  58,  61,  80. 
Forcing,  121,  122. 
Forests,  196-204. 
Foundations  of  society,  192. 
Freezing,  89-92. 
Frost,  89-92. 


INDEX 


215 


Fruits,  67,  60,  155. 
Functions,  21,  22,  23. 

of  roots,  24. 

of  leaves,  58. 

of  stems,  93,  96. 
Fungi,  47,  48,  77,  104,  111. 

Gametes,  14^-144. 
Gametophyte,  143-145. 
Gas,  120. 

Gases  used  by  plants,  57. 
Gemm£e,  138. 
Generations,  7,  141-145. 
Georgia  oak,  130. 
Geotropism,  of  roots,  4,  38,  39. 

of  leaves,  74. 

of  stems,  74. 
Girdling,  103,  104. 
Glands,  79. 
Gleditschia,  123. 
Grafting,  177,  178. 
Grape,  95,  105. 

Gravity,  influence  upon  roots,  39, 
40. 

upon  leaves,  74. 

upon  stems,  128,  129. 
Growth  of  roots,  49. 

in  darkness,  03,  65,  122. 

of  leaves,  87. 

of  stems,  108,  109,  111. 
Gum  arable,  44. 

Hairs,  71,  84. 
Heliotropism,  73. 
Hemlock,  198,  200. 
Hibernacula,  119,  120. 
Hickory,  110,  198. 
Holdfast,  20,  153. 
Honey,  78,  202. 
Honey  locust,  123. 
Hop,  126. 

Horse-chestnut,  86. 
Horse  radish,  133. 
Humus,  37,  38. 


Hyacinth,  25,  28,  121. 
Hyacinthus,  27. 
Hydrogen,  16,  18,  64,  183. 

Indian  pipe,  47,  77. 
Insects,  161,  152. 
Iodine,  16,  19,  167. 
Ipomea,  49. 
Iris,  56. 
Iron,  16. 

Iron  chloride,  18. 
Ironweed,  205. 
Ivy,  65,  86. 

Jack-in-the-pulpit,  27,  121,  123, 140. 

Lamina,  54,  72,  73,  81,  85,  86. 

Laminaria,  26. 

Larkspur,  95,  148. 

Leaf  mosaic,  72. 

Leaf  traces,  95. 

Leaves,  12,  54-92,  123,  179,  180. 

Lemna,  30. 

Lichens,  207. 

Life,  length  of,  112,  113,  114,  115, 

131,  155. 
Light,  influence  upon  roots,  40. 

upon  chlorophyl,  01-63. 

relation  to  plant,  61,  195,  196. 
Lily,  135,  148. 
Line,  14,  16. 
Liquid  air,  185. 
Liquid  hydrogen,  185. 
Liverworts,  50,  80,  136,  193,  200. 
Loosestrife,  135. 
Lunularia,  138. 

Maize,  165-172. 

Mangrove,  29. 

Man  of  the  earth,  49. 

Maple,  3,  4,  6,  19,  68,  81,  86,  95, 

96,  101,  105,  198. 
Marchantia,  51,  55,  136,  138. 
Meadow  garlic,  135. 
Meadows,  204. 


216 


INDEX 


Melon,  90. 
Mesophyl,  55?  82. 
Mlcrampelis,  126. 
Midrib,  55. 

Mineral  coatings,  12-14. 
Mint,  94,  95,  99,  100. 
Mistletoe,  45. 
Moisture,  154. 

influence  upon  roots,  40. 
Monotropa,  47. 
Morning  glory,  112,  126. 
Mosses,  4,  7,  50,  80,  143,  193,  200, 

203,  205. 
Moulds,  76,  77. 
Movements,  of  roots,  38-43. 

of  leaves,  73-75. 

of  stems,  74,  112. 

sleep,  85. 
Mullein,  85. 
Mushrooms,    51,    52,    76,   77,    186, 

201. 
Mycelium,  52. 
Mycorrhizas,  47,  48,  104. 

Naked  buds,  116. 
Narcissus,  63,  112. 
Nerves,  55. 

Nitrogen,  16,  57,  61,  64. 
Nodding  movement,  112. 
Nodes,  49,  94. 

Oaks,  4,  68,  95,  110,  198. 
Offsets,  21,  133. 
Oil,  19,  154. 
Onion,  121. 
Orchid,  48. 
Organs,  22,  23. 
Ovary,  148,  158. 

Oxygen,  16,  18,  57,  61,  64, 152,  183. 
185,  186,  187,  188,  189. 

Paired  seeds,  172-174. 
Palm,  29,  111,  156,  162, 

Pansies,  85. 


Parasites,  45,  77. 

Parasitic  roots,  45. 

Passion  flower,  126. 

Path  of  sap,  103. 

Pea,  39,  49,  56,  75,  178,  186,  190. 

Peach,  67,  90. 

Pelargonium,  116. 

Peony,  67. 

Perennials,  156. 

Petals,  85,  147. 

Petiole,  64,  72,  78,  81,  101. 

Phosphorus,  16. 

Pine,  4,  87. 

Pine  sap,  77. 

Pistil,  148. 

Pitchered  leaves,  77,  78. 

Pitcher  plant,  78. 

Pith,  90,  98,  167. 

Plaster  of  Paris,  18. 

Plum,  67. 

Plumule,  161,  172,  179. 

Poison  ivy,  123,  124. 

Pollen,  147-152. 

Pollination,  149-151. 

Polypody,  130. 

Pond-scum,  4,  53,  80,  120. 

Pond-weed,  14,  119,  208. 

Poplar,  4,  81,  110,  133. 

Position  of  leaves,  72,  73. 

Potamogeton,  14. 

Potassium,  16. 

Pressure,  by  growing  roots,  42. 

by  expanding  cells,  190. 
Primula,  85. 
Protection,  of  roots,  43. 

of  leaves  and  stems,  122,  123. 
Protein,  18. 
Protoplasm,  1,  2,  3. 
Puff-balls,  201. 
Pumpkin,  126. 
Purposes  of  plants,  3. 
Putty  root,  130. 

Quercus  Georgiana,  130. 


INDEX 


217 


Radish,  32,  41. 
Raspberry,  137.' 
Red  color,  65-70. 
Red  maple,  5,  6. 
Reproduction,  131-137. 
Respiration,  184,  185. 
Rliacliis,  56. 
Rhizoids,  50,  141. 
Rhubarb,  65,  102. 
Rock  societies,  206. 
Root-cap,  42,  43. 
Root-hairs,  31-36,  89. 
Roots,  24-53. 
Runners,  21,  137. 

Salix,  15. 

Salt,  18,  157. 

Saprophytes,  77. 

Sarracenia,  78. 

Saxifrage,  200. 

Scaly  buds,  116. 

Scouring  rush,  13, 

Scutellum,  168. 

Seaweeds,  26. 

Seed-coats,  158,  159,  167,  172,  177. 

Seeds,  21,  131,  154-181. 

Sensitiveness,  of  roots,  36-43. 

of  stems,  127-129. 

of  tendrils,  126,  127. 
Shellac,  44. 
Shrinkage,  of  leaves,  12. 

of  roots,  27. 
Silicon,  13,  16,  123. 
Silks,  166. 

Sleeping  buds,  118,  119. 
Slime  moulds,  2. 
Smilax,  171. 
Societies,  191-201. 
Sodium,  16,  17,  18. 
Soil,  composition  of,  30,  31. 
Sorghum,  19. 
Species,  6. 

Spectrum  of  chlorophyl,  60. 
Spines,  122. 


Spirogyra,  53,  209. 

Spongy  layer,  45. 

Spores,  21,    52,  131,  139,   140,  141, 

142,  145,  149,  184. 
Sporophyte,  142-146. 
Spring  beauty,  148. 
Squash,  26,  126. 
Starch,  19,  154. 
Stems,  93-129. 
Stigma,  147. 
Stilt  roots,  29. 
Stinging  hairs,  122. 
Stolons,  137. 
Stomata,  55,  82. 
Storage  in  roots,  48. 
Strawberries,  90,  137,  138. 
Struggle  for  existence,  124,  125. 
Styles,  147. 

Sugar,  18,  19,  35,  36,  65;  66,  106. 
Sugar  maple,  4,  5,  6,  154,  184. 
Sulphur,  16. 
Sumach,  56,  58. 
Sunflower,  12,  24,  26,  33,  100,  109, 

131. 
Sweet  potato,  132,  133. 
Sycamore,  4,  110. 

Tannins,  19. 

Temperature,  89-92,  154,  195. 

Tendrils,  126,  127. 

Thallus,  128,  197. 

Thistle,  1,  123,  205. 

Thorns,  122. 

Tissues,  22,  23. 

Toadstools,  51,  201. 

Tobacco,  90. 

Tomato,  25,  34,  40,  45,  67,  83,  96, 

103. 
Touch-me-not,  102. 
Transplanting,  89. 
Transpiration,  81-85,  88,  89. 
Tubers,  133,  134. 
Tulip  tree,  68. 
Turnip,  11. 


218 


INDEX 


Utricularia,  66,  78. 

Vallisneria,  208. 
Vaucheria,  210. 
Vegetative  reproduction,  132,  133, 

139. 
Velvety  surfaces,  85. 
Violets,  4,  5,  6,  85. 
Virginia  creeper,  66. 

Walnut,  4. 

Water  cultures,  15. 

Water  hyacinth,  30,  43,  208. 

Water,  in  plants,  10. 

in  leaves,  81. 

in  protoplasm,  90. 


Water  transpired,  82,  83,  84,  85. 

Water  lily,  120,  20ar. 

Wax,  84,  176. 

Weeds,  125. 

Wheat,  7,  155. 

White  surfaces,  61. 

Wild  garlic,  135. 

Wild  onion,  135. 

Willow,  15,  41,  55,  132,  207. 

Wilting,  83,  34,  88,  97. 

Wind,  150,  196. 

Winter  buds,  119,  120. 

Witch-hazel,  203. 

Wood,  98,  99. 

Xanthium,  171-175. 


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LESSONS   WITH   PLANTS 

Suggestions  for  Seeing  and  Interpreting  Some  of  the  Common 
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By  L.  H.  BAILEY 

Professor  of  Horticulture  in  the  Cornell  University 

With  Delineations  from  Nature  by  W.  S.  HOLDSWORTH,  of  the 
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Professor  of  Botany  in  the  University  of  California 

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